REMINDER V1.20 has an Installer 7 script which takes care of the whole installation. If you don't have Installer , Commodore has made it freely available, so it should be found on many ftp sites. If you can't find it, then you'll have to install REMINDER from shell.
Make sure Installer is in the AmigaDOS path (C: is where I have it), then double click on the Install-Reminder icon. The script installs REMINDER and REMINDERCHECK , ReqTools.library8, documentation and ARexx examples, asking you for confirmation if you don't select the Novice user level.