First, is this based off of the Outlaw winner from a year-n-a-half ago? (https://dtdb.co/en/decklist/2107/kill-trol-clowns-kill-and-control-2016-great-maze-outlaw)
Second, does the dude you unboot have to be in the shootout?
Text:"Shootout, Boot: Choose an opposing dude. Boot that dude, and you may give them +5 value. If that dude's grit is 11 or higher, you may unboot one of your other dudes."
Yes. Shootout abilities must target cards in the shootout. The exception is when the card would bring something into the shootout.
More detailed in the rulebook.