You use double nocking points and nock between them (I use the brass ones, but have used served on string nocking points for this too). Make sure they are where you want them because if you decide to change the nocking point you have to cut off the 2nd and 3rd serving and start over. For the top finger (shooting split finger) start your second serving 1 1/2 inches or so above the top nocking point, serve under, then serve down to the top nocking point, keep serving and you'll find the serving jig reverses when it hits the nocking point and serves now up, giving the 3rd layer of serving. You may have to manually serve the last 1/16th or 1/32nd inch to the nocking point if the serving jig wants to start back up too soon. When you reach nearly the start point of the 2nd serving (ie 1 1/2 inches above the nocking point) serve the tag end under. No need for knots, you just serve under like you would on the 1st serving of a bare string. For the bottom 2 fingers its the same deal, just start serving maybe 3 inches or so below the bottom nocking point. I just do it by eye, so measurements are approximate. I put a small dab of contact cement at the end of the serve-under, just like for serving a string.
If you don't know how to serve a string this might be confusing, but if you have served regular strings it should make sense. Watch a youtube on serving a string and you'll see what I mean.
I wouldn't pay anyone to serve my strings...buy a jig and a spool of serving thread for a few bucks and learn how. Takes about 5 minutes when you know how, gives you something to do when you're sitting in front of the TV.
R