The passwords used for logging in to accounts in Safe Mode are the same ones used while in normal "mode" Windows. So login to any admin account in normal Windows, access the Control Panel-User Accounts and manage the other account (change the password) you're using in Safe Mode.

Unfortunately, you've not told us which version of Windows you're using but it it's Windows 10, and if you're using a Microsoft Account login while in Safe Mode vs the standard local login, the instructions in the link below should help you get it done.

Hope this helps.