Hello Jun Jian Chen,
If you accidentally logged in with your client’s email as the Windows administrator account, you can change the admin email by switching the Microsoft account associated with that profile. The simplest way is to go into Settings > Accounts > Your Info and select the option to sign in with a local account instead, or to add your own Microsoft account and then promote it to administrator.
Once your own account is added, you can safely remove the client’s account from the administrator role. If you prefer to keep the existing profile but change the email, you’ll need to disconnect the current Microsoft account and connect your own email address. This ensures that future authentication, OneDrive sync, and Store access are tied to your email rather than the client’s.
It’s important to back up any files or settings before making the switch, especially if the client’s account has been used for work. After the change, confirm that your account has administrator rights by checking under Settings > Accounts > Family & other users.
I hope the response provided some helpful insight. If you find this answer useful, please hit “accept answer” so I know it addressed your concern.
Jason