If you've given up guessing the password, you can do one of two things based on which user profile was affected.
If it's a secondary user, not the owner profile, you can just delete the profile you forgot the password for while logged in to the owner profile and start a new one.
If it's the owner profile you will have to do a factory reset. Here's how you can do it if you don't already know how. It's under "With your phones buttons (advanced)". I've never done it this way with GOS, but it should be the same as Stock. Ignore the part that says how to get ready for the reset. You won't be prompted for any passwords on GrapheneOS to do a factory reset.