After Humans 1.12.2 updated to version 1.6.4
Removed RFTools Dimensions
Removed Version Checker
Type in the modpack name (After Humans 1.12.2) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select After Humans 1.12.2 from the list on the left. The launcher will handle everything else!