Open the Settings App.
Go to Accounts - Your Info.
On that settings window, is there either an option to 'Switch to a Local account' or an option to 'Stop automatically signing into apps with this account'.
If either option exists, select it, that will switch your Windows login to a Local account, then you can add the details ot the other Microsoft account.
Please Note, if you switch the login account to a different Microsoft account, any apps you downloaded for the Microsoft Store may not work on the new account, also, any files you may have synced to OneDrive, will not be accessible on the new account, because they are stored online on the other Microsoft account.