Stop operating the door
A garage door is balanced by its springs. When one breaks, the full weight — typically well over a hundred pounds — transfers to the opener and to whatever is holding the door up. Running the opener in that state strips the drive gear, bends the track and, in the worst case, lets the door come down unevenly.
Take the opener out of service until the spring is replaced. If the door is stuck open, do not pull the emergency release cord.