You can download AIM from all over the web, such as download.com or oldversion.com or whatever, if you use Windows 10 or 11 then you may want to use version 5.0 or lower of AIM. If you use the patcher after installing it, it'll get it setup for you. You just login with the same username and password as you do MSN, just remove @escargot.chat
The patcher:
https://escargot.chat/patcher/