If you're missing channels or perhaps have a gimpy indoor antenna that only works when you stand there holding it like a one-legged scarecrow, the explorer tool can help find a clearer signal or missing channels.
1. Go into TV > Explorer, select your device at the top and either select your existing frequency set, or you can grab one from the library or make a new one from scratch.
2. Hit Try Lock on a frequency that you know should be correct. If your frequency isn't listed, scroll to the end of the list and add it in.
The explorer is going to keep trying to lock the signal every 5 seconds or so. Most tuner drivers (the half decent ones anyway) will keep trying to acquire a signal whilst you fiddle with your antenna. When it locks, you should see channel preview thumbnails stream in.
3. Use the green signal metre to get the best strength you can. Again, not all drivers are well behaved, some may return 100% lock or 0% and nothing in between, other drivers are written correctly and give you fine-grained sensitivity so that you can actually test your signal.
When you have channel previews coming in simply right-click any of the channel boxes and Add all channels to > Any list you like. Or, now that you've fixed your antenna, you could hit Scan on the left to rescan all of the frequencies and it'll automatically add any new channels found into the EPG.