If you found that with adho mukha svanasana,or downward-facing dog, that this keeping this external rotation in the shoulder was difficult for you, there's another posture entirely, and it's dolphin dog.
You can use a block and you bring that, try the other hand that we talked about before in down dog, to the block, to the corners of this block. Bring your forearms to the floor. From there, you can walk your knees back, tuck your toes under, lift your hips up, and hang up here.
So, pressing the forearms down to the floor, shoulders should be over the arms in a comfortable position, but the belly scoops in and up and the backs of the legs start to expand, and the head can just let go, let go, let go. So this is a variation on the downward-facing dog.