Read through the “System Mode” section of the manual…starting on pg. 46 Especially the section on setting up the Aux Switch. I posted a link to a little video showing how to work in system mode. I would search YouTube I’m sure there’s more videos about working with the TF.
FYI about the “Learn” function & making sure there are not other parameters already assigned to a switch.
P.S. I was reading my earlier post and I hope it didn’t imply you had to get just a two button unit.