Using one of the 365 subscriptions, can't get office to recognize the person it is shared with.

Question

I have a current subscription to Office 365; I sent a share to my husband. He successfully downloaded 365 to his computer. However, the computer he uses once belonged to another family member who had MS Office over 10 years ago, so when trying to use the current, paid-for 365 apps, even if he changes the email address, 365 defaults to the previous family member from 10 years ago (listed as admin). Multiple tries, no joy. We can't access 365 apps; we are only offered to purchase again. Suggestions are very welcome as to how to be able to use 365. Thank you for your time.

Working on a PC with Windows 11. Chrome browser.