I’d just add the pistol shrimp near to the goby and they’ll likely find eachother at some point. I did that when introducing my pistol shrimp to my previous yasha and it worked the same way when I introduced my new yasha to the same pistol shrimp.
P.S. These guys aren’t true Watchmen Gobies - The true Watchman’s are from the genus Cryptocentrus whilst wheeler’s gobies are from the Venus Amblyeleotris.