Could be CH26 or 18RP I don't remember what it is on that radio even though I have a couple.
Don't worry about the offset, as long as you are on a repeater channel, the offset is already set.
Forget about Zello.
Request the tones from the owner.
Once you have the tones, read the manual for how to set them on the radio.
You can also use the CPS which is easier than manually programming.
At this point, if you have a problem, start a new thread describing exactly what you have done and what problem you have encured.