first off dont use repeater to issue commands. you only want to use that for when you need to move the mouse in all windows at the same time (chat cut scenes for example). or type something in chat all at the same time etc

so what exactly isnt working?

The basic setup is to create a 2 step mapped key.
In step 1 create a keybind that corresponds with selecting "party member 1" this keybind needs to be setup both ingame and isboxer

in step 2 setup the keybind for follow. remember to select the keybind used in game

in the mapped key description you created, select from the dropdown "press or release".

So if done correctly, pressing down selects party member 1 and releasing follows him.