Cut all broken branches back to the last healthy branchlet or crotch. Remove everything broken. Once that's done, if you still have a large hole in it where little light will penetrate, thin out the surrounding growth, and head it back. This will promote regrowth, and let light in to where the broken branches were removed, allowing stronger regrowth in that area. Expect a good covering or regrowth the first year (if your bush is healthy), but it will probably be a few years until the area has filled out again.
If you want, you can head back the rest of the bush the next season, so that it looks more symmetrical, but don't do this the first year, as you want to encourage as much regrowth to the damaged area as you can the first year.