Hello
Go to https://account.live.com.
Then go to Security > Manage how I sign in
Click on Sign out everywhere. This is intended to disconnect any active sessions that may still be connected. Please note that this can take up to 24 hours to fully take effect.
Unfortunately that’s all you can do remotely, not sure how your files were synced, if they were synced into local copies your files are still there and there’s no way to remove remotely.