I know this is maybe not the answer you want, but if you are just interested in getting the job done there exist companies that are experts on this, for example:
The first thing that is required is to define what they are trying to do. In other words, list some question and answer examples. It's amazing how many people are unwilling or unable to do this and just jump to "we need to train a custom model". To do what exactly, or answer what kinds of questions? I have actually had multiple clients refuse to do that.