Compuserve is now a subsidiary of AOL. So when you will go to login you have to visit AOL official website or you will be redirected to this website. You need to have your mail or username and mobile number which you have used in registration process. If you want to know more you can read this guide.
For more details visit - https://onlinehubb.com/compuserve-mail-login/
For more details visit - https://onlinehubb.com/compuserve-mail-login/