what part of "minimal required version = 3.3.0 / 4.3.0" did you not understand ;)
the easiest would be if you had a db backup, just restore the backup, and restore the 3.1.1. version of the module. If you dont have backups available, you can try a "downgrade", if you have access to the db, locate the table "desktopmodules" and locate in that table the row for the Announcements module. Reset the version to 00.00.00, and reïnstall the dnn 3.1.1. announcement module (that would be announcements version 3.1)
you might loose data in the announcements module, be sure to keep a backup of the data, so you can manually add the data back if needed.
good luck