A guide would be something like:
Find the control channel and run it for a bit to establish some of the system information. Look at RadioReference to see if the system is there. If not...
Populate the .Network file with the system information. Tier III uses Area Length as an additional field. 5 is the default area length so I suggest using that:
TIII, 1, "big radio company", 5
You can also populate the .Sites file with what info you have so far. Your system may show different info once you have populated the Area Length into the Networks file. It should show Site info as 1.1, 1.2, etc. Your example has 4 sites (3 Neighbors) so:
TIII, 1, 1.1, "North"
TIII, 1, 1.2, "South"
TIII, 1, 1.3, "East"
TIII, 1, 1.4, "West"
To gather information for the .Frequencies file, you need to determine if the channel numbers are band plan based or picked by the company. If you see something like 345, 512, 633 these are very likely Band Plan based. If you see something like you have, 27, 35, 37 those are random and require more work. If you are in a country that shows the licensing data online, you can take the control channel information and go searching. Otherwise, you need to do some searching. You can start by putting the CC into the .Frequencies file. We don't know the channel number so use the "?" for a placeholder for now. Replace the xxx.xxxxx with your control channel. You only need to populate the odd channel numbers. Also, you don't need to enter a frequency for RX Frequency.
TIII, 1, 1.3, ?, xxx.xxxxx, 0.0, 0
You can set up the other channels while you are editing this file. Simply use a semicolon to prevent the program from using the line yet.
;TIII, 1, 1.3, 27, yyy.yyyyy. 0.0, 0
;TIII, 1, 1.3, 35, yyy.yyyyy. 0.0, 0
;TIII, 1, 1.3, 37, yyy.yyyyy. 0.0, 0
You can also add some info for your Neighbor Sites while you are here as well:
;TIII, 1, 1.1, 3, aaa.aaaaa, 0.0, 0
;TIII, 1, 1.2, 21, bbb.bbbbb, 0.0, 0
;TIII, 1, 1.4, 41, ccc.ccccc, 0.0, 0
Run the program and look for traffic on the Channel Activity window. When you see an activity spike, click on it. watch for matching information such as system type, TIII, channel numbers, talk group numbers, even color code info. If you get a confirmation on a frequency, edit the .Frequencies file and see if the program follows a conversation properly.
Be patient and make lots of notes. Don't be afraid to test guesses