When Cody was a puppy and could carry him I took him down the the spot I wanted to use (all the while repeating "Cody make ....."as I was even opening the door)and put him down
and just kept repeating it followed by "good boy'" if he moved, I just put him back to the spot and afterwards gave him a treat and
repeated "Good Boy made ......" honestly took about 10 days or less, as small as he was. Now I just put him on a 40ft leash and he heads to his spot. of course he sometimes strays-all the while looking back at me (laughing I'm sure!) but 99 % of the time he's as good as gold. Good luck!