This happens, and there is usually a way back. Which way depends on which of the two secrets you have lost, so start there.

Which one have you lost?

Relic has two secrets and they do different jobs:

Your account password: Signs you in to your Relic account, the same way any website password does. We can reset it by email.
Your vault passphrase: Unlocks your items on a device. It never leaves your device, so there is nothing on our side to reset.

If Relic is asking for your account password on the sign-in screen, read the next section. If it has already signed you in and is now asking to unlock your vault, skip ahead to the recovery kit. The sign-in screen says the same thing under the Forgot password link: This resets your account password only. Your vault passphrase is separate; if you lost that, use your recovery kit.

Resetting the account password

Type your email first
The reset needs to know where to send the link. If the box is empty Relic says Enter your email above, then tap Forgot password.
Press Forgot password?
It sits under the password box on the Sign in screen.
Open the email
Follow the link and choose a new password. Check your spam folder if it has not arrived after a few minutes.
Sign in again
Relic will then ask you to unlock your vault. That is the other secret.

Your items are untouched by any of this. The account password protects the door to the account; it is not what your items are sealed with.

Using your recovery kit

The recovery kit is a block of text Relic gave you when you made your vault, and told you to save. It is the way back in when the passphrase is gone. When Relic asks you to unlock, the third door on the screen is the one you want.

Sign in
Email and account password as usual. Relic then shows Unlock your vault with three doors.
Choose I lost my vault passphrase
Its second line reads Use your recovery kit.
Paste the kit
The screen is Use your recovery kit: Paste the kit you saved, then set a new vault passphrase. Paste it into the Recovery kit box.
Choose a new passphrase
Fill in New vault passphrase and Repeat the vault passphrase, then press Unlock. From now on that is your passphrase.

If Relic will not take the kit, it says which problem it is:

That doesn't look like a Relic recovery kit. You have pasted something else. A kit starts with the line relic-mk-v1, then a line with your email, then a row of short groups of letters and numbers. Paste all three lines.
That recovery kit looks mistyped. Check it and try again. The kit is nearly right, so a character is wrong. Copy and paste it rather than typing it.
Passphrases don't match. The two passphrase boxes differ.

Once you are back in, look at Settings › Sync and account › Security and press Show recovery kit to save a fresh copy somewhere you will find it. More in Your recovery kit.

Using a device that still works

If any of your devices is still unlocked and syncing, you do not need the kit at all. That device can let the new one in.

On the working device, start the pairing
Open Settings›Sync and account›Add a device. It shows a QR code and a pairing code.
On the locked-out device, choose Use another device
It is the second door on Unlock your vault: Type the pairing code shown on a device you already use. On a phone you can point the camera at the QR instead.
Check the code matches
Both screens show a short code. Make sure they are the same, then approve on the device that started it.
Set a passphrase you will remember
Once the new device is in, go to Security and press Change vault passphrase. Its line reads Re-wraps your key. Your recovery kit stays valid. When it is done Relic says Passphrase changed.

Pairing in full, including what the codes are for, is in Add a device.

If both are gone

If the passphrase is gone and the recovery kit is gone, the sealed data cannot be opened. Not by you, and not by us. There is no back door and no reset. That is the point of sealing it this way, and it is the honest answer.

What you can still do:

Keep what is on your devices. A device that is still unlocked still has your items and can still show them to you. Export them before you change anything: Settings › Vault and storage › Export vault.
Start a fresh vault. In Settings›Sync and account›Security there is Delete account, described as Permanently delete your synced vault and account on our servers. You type your email to confirm. Local history on your devices is not deleted. If you pay for a plan, cancel it first.
Ask us to close the account if you cannot get into it at all. Write to support@relic.space from the address the account uses. We can remove the account and its sealed data; we cannot open it or send it to you, because we do not have the key.

When you set the new vault up, save the recovery kit on the way past. Relic shows it once and says why: The only way back into your data if you forget your vault passphrase. We cannot recover it for you. Print it or store it in a password manager.

Background on the two secrets and what is sealed with what is in Your vault passphrase.