Where did break? If it broke flush with the manifold, take the manifold
off and grab the remains with pliers or locking pliers and remove it.
Buy a new bolt, you're good to go.

If it is broken flush with the head, since it broke putting it back in,
with the manifold off you should be able to get the remains out. There
won't be any torque on it so you should be able to turn it using a screw
driver or whatever you can push along a edge or divet or whatever. A
dremel to make a slot in it and then a screw driver can work too.

It's when bolts break on the way out that it's a disaster. On the way in
usually works out ok because the threads are binding because of
corrosion etc...  (self tapping screws are another story... )