This thread will probably get moved by an admin, but here's an answer for now.
(Please see the attached images if this is not clear.)
Open the Minecraft Launcher.
Click "Launch options" in the upper right.
Click "+ Add new" to create a new launch profile.
For "Name", give the profile a name that will make sense to you.
For "Version", click the dropdown arrow and select "release 1.12.2"
Click "SAVE".
Click "News" in the upper left.
Back on the main Launcher screen, click the arrow to the right of the "PLAY" button.
Select the new launch profile you just created for 1.12.2 .
Click the "PLAY" button.
Famcraft ahoy!
