If you don't have any good key codes, the normal process is to erase the old codes, and then any key will work without further tools. The new Forscan etc, devices and components, have their own procedures I'm not sure about. I doubt they simply add a new key code in, maybe they do. The ideal thing would be to erase the PATS module of all codes.
When the PATS is empty, anyone can add a new first key, the normal programming method will work(minus the use of a prior keys). The 1st key is added most easily and quickly. Then a 2nd key will require the 1st be inserted as described in the programming procedure, and then the new 2nd key. After that, it requires two proper key codes plus any new key being added.
So look into the Forscan and ELM etc, items. You will benefit from them for other things later for sure. At a total price that sounds like under $40, everyone should have those and be getting used to what they can do.