There are a lot of bad personal trainers out there. I would def try and figure things out on my own a little bit. Plus personal trainers will have you changing shyt up all the time to keep you coming back and feeling like you need them to tell you what to do.
Really, you can just get away with a simple ass program. A nice little upper body/lower body split. Upper body day, you would just do
Bench press
Some kind of back move (chin ups, lateral pulldowns, dumbbell rows)
Lateral raises
Tricep isolation move
Bicep isolation move
Then for lower body I think you could just get away with
Compound quad move (squats, leg press, whatever, doesn't really matter)
Compound posterior chain move (deadlift variation)
Quad iso/accessory (front squats are prob best)
Hamstring curls
Calf raises
You hit those for 3 sets of 8-12 reps 2x a week each, focus on form and progressing in weight, and eat a high protein diet with a reasonable surplus (no more than 1lb a week in weight gain) you will be straight. You dont need a personal trainer for anything but maybe teaching you movements... and a lot of em dont' know em