While doing some work, somehow the first 1-2 lines of thread in the front of a hole got mashed and wacky. 95% of the bolt hole is fine, and intact. The stock bolt doesn't go in all the way through the threaded area, maybe uses 60% of it, so to keep the same strength of bolt, we will just use a longer one in its place.

What is the proper method to clean the begining threads, without redoing the entire hole? Would you first use a ream to cut the bad threads out, then use a tap? How hard is it to "connect" with the good threads again with the tap, without starting a cross thread. This hole is not easily drill and fully retapped, so that is out of the question for now.