Hi muming
What is done depends a lot on the situation so it is a little difficult to say what I would have done for you. However here is a few things that we can try to help baby out

Position change:
Often just getting mum to change position will change the shape and size of your pelvic space and let that baby out. This would usually be my first choice.
Knees to chest
This also opens your pelvic space and again can help to give baby a little more room.
I could press on your tummy and try to push the baby's shoulder under your pubic bone.
I could put my fingers inside you and move the baby’s shoulder
I coul put my fingers inside you and pull the baby's arm out first this will help bring the shoulder out.

There are a couple of other things that could be done as a last resort, but these are a little vicious and perhaps best no discussed here.