This 30-day delay is intentional. It’s a security safeguard designed to protect users in case someone else tries to hijack their account by changing recovery info. The wait gives the rightful owner time to notice and stop unauthorized changes.
Unfortunately, this policy cannot be bypassed or expedited. You can read more about it directly from Microsoft here:
If you must use the computer now, the only option is to clean install, sign in with a different account or local account for now, then wait 30 days, link your own account after that. However, doing so you do lose all the files saved on the computer.