The latest version 1.7.31 is available for download here on itch. You can delete the old folder and just download the new version, extract and use as normal.
If it is showing you a Buy Now button instead of download options I would check the account is the correct one, and if so then contact itch support to find out why it is no longer associated with your account.
I can see your username on my webserver, so I can see you have used the app in the past. I am not able to manage what itch does and doesn’t have in its database for your purchases though. Sorry I can’t help more.