You don't have to turn anything on in a menu for this. Nor can you have IR and UHF enabled. It's one or the other. Procure another 21.x uhf remote.
Make sure the number tab at the bottom is flipped to the '1' side. It just pulls straight out the bottom.
Make sure the IR/UHF switch under the battery cover is on UHF.
In the receiver, menu, 6 1 3, yes
With new remote
Hold SAT til all the lights light up.
Enter a number between 1 and 28
Press #
Wait for sat to blink 3 times
Wait 1 or 2 seconds. Press record.
Address on tv1 should be changed to uhf with the number you chose