The security passcode on your reMarkable can only be reset from the Security settings menu, but you do have an unlimited number of attempts to unlock your device if you have forgotten your passcode.
However, after several incorrect passcode attempts, you will get a lockout timer that will prevent you from trying again. The lockout timer also increases for each failed attempt, to a maximum of one hour.
You can factory reset your device if you forget your passcode. If you try the wrong passcode too many times, then you'll be able to reset your device by following the instructions on the device and visiting my.remarkable.com. Use your email address and password for your cloud account to log in and reset.