How to forget and restore accounts?

Forgetting an account is not the same as deleting your account. It works similarly to traditional logging out with the caveat that forgetting removes your account from view in the signer. It does not delete your account from the network. You can always recover your account and bring it back to the signer as long as you remember your secret phrase (and derivation path for derived accounts) or possess the designated JSON file and remember password you have set.