The Trick in a Nutshell:
Step 1: Run initial set up. Enter home zip code, Enter Secondary zip of neighboring DMA.
Step 2: Run initial set up again. Enter home zip code, Enter third (4th, 5th..) zip code.
The third, forth, etc zip codes can be for a 3rd DMA OR a DMA that has a PSIP channel that is that of your missing zip.
Example: Locally, WUVC is 40-1 Univision, 40-2 Unimas, 40-3 Bounce, 40-4 Gettv. Only 40-1 and 40-2 are in the database, but I added a Los Angeles DMA zip and it added 40-3 and 40-4. The guide data is for TBN's subchannels in LA, but you can at least tune to the missing channel. Each time you add more zips, it adds to the list, not deleting anything from it.
Research can possibly match forced zips with subchannel networks that match (example, if your city has Antenna TV on 8-2 but your local channel is not in the database, you could luck out and find another Antenna TV on 8-2 to match guide data most of the time. It's time consuming. Cococut13 has great helpful posts about this throughout this and the "other" forum. The "other" forum also has the database in an excel sheet.
It sounds crazy. It works. I added 16-5 from Montana, 20-4 from Salt Lake City, 22-2 / 40-3 / 40-4 from Los Angeles, and 43-3 from Fresno to complete my guide, using west coast zip codes so the "K" stations are the ones with incorrect data which, for some reason, makes me feel better. It is less confusing to say to someone "The channels that start with K are wrong guide data." I was not able to add 16-6 because there is no 16-6 in the database.