No password access with free account

I have a free TeamViewer account, which I have had for years. My only use for this is to occasionally access my very elderly father's computer when he has a problem. We set this up years ago so I could login with his account password (he is almost always there when I log in, but finding the little icon and opening it up and reading the password is challenging from his point of view, and ... he is about to be 98, who knows whether I might need access to pay his bills or something when he is not there). So he has a new computer which I set up for him a couple of weeks ago. I can get into it if I get him to read me the password (or from my iPad when I am sitting in front of it), but I can't figure out how to get it working with the account password (or a different standard password), the way I had it on the old computer. I started to review the documentation, but it is targeted for uses so very far beyond my own. Could someone direct me towards a reasonable practice for this need? A link to a particular page in the documentation might do it, or a suggested approach with a search term. TeamViewer says it is 15.7.7. We are both on Windows 10 PC's, if that matters.