You can't. Unown is the least viable fully evolved pokémon in any competitive format in the history of pokémon. With only Hidden Power it just doesn't even have a movepool to surprise anyone with anything unorthodox. Unown simply doesn't have any redeeming factors competitively. Its stats are horrid, its movepool is literally the worst in all of pokémon, its typing is nothing spectacular, and its ability is no Wonder Guard either.
To put it quite simply, if you somehow managed to enter a level 100 Unown into a level 50 format, it still wouldn't be all that great. Unown is simply so terrible that even at double the level of everything it's fighting it still can't do too much.