Easy way is to get one of the Software packages (some are free) or get the BUTEL software if your specific scanner is Programmable via USB cable.
Then you can either manually enter Freq or Trunking maps (hardest way) or download via Radio Reference if you are subcribed - that is the most easy solution and the cost is less than $100. total and then you can add/delete at your own pace...
A lot better long term solution in my view...