cybermind Hi there, if you have forgotten your password, you will need to factory reset from recovery mode GUI, which you can reach using the hardware buttons.
other8026 has provided a link with further details.
A factory reset will return your device to a fresh install of your current version of GrapheneOS, so there is no need to update after a factory reset, unless of course, you weren't on the latest version before the reset.
other8026 I am not too sure what the best route forward would be, but you will either have to factory reset then update multiple times (possibly 10s+ of times), or you would factory reset, then flash GrapheneOS again to the latest version.
Reflashing the OS or making multiple updates is not required. After a factory reset a GrapheneOS device remains on the same version as before the factory reset - the version is not rolled back.