Hello, this is Emily.
It sounds like the computer is domain joined and credential needs to be verified against AD.
It is normal for remote app not to show the UAC sign in page to the remote user, but the local user could see the pop up box asking for admin credential.
The problem here is that the remote computer is not connected with company server to check against AD. How long ago did you log into that computer? What's your company's cache credential expiration policy? If it is still within expiration, try the old password you used back then as it might be still cached.
Otherwise, a standard user will not be able to change another user's password on the computer locally.
The computer should still have a local admin user though. Do you know the credential of that local admin user. This is not your domain network admin user. If you know it, for username, key in:
computername\username
(replace computer name and user name accordingly). Then the password.
=============
If you cannot do any of this, the user should connect to company VPN, or bring the computer into company network in order to get it fixed.