"we have a message VHF L Antenna Fail". I wanted to provide the Ground Engineer with something to tell the flight crew about what he was going to do, ie, "I am going to check the MEL"
3 installed 2 required, no maintenace procedure, see you next time!
Very unlikely that on the headset that you will have an MEL to hand, the crew do, so the only thing to do is get them to check. The rest is really down to experience, which is hard to teach.
If I had the above, I would get them to cycle the cb, try again, if still no good, their call, they can go with it.
If like you say communication is difficult, either have an engineer on the other end of a radio who can come to the a/c, or leave it up to the crew.