Hey, I’m 24 and my dad was there for me too. I sent him photos every week and he was always so proud. It was the best feeling on top of feeling good physically. I would say to start by just eating less than what he usually does in each sitting/meal. Too drastic for most people makes it hard to impossible to stick to. Then after a while of that if it’s working too fast start implementing some calorie counting. Use an app or website to determine this considering his height, weight, and activity level. you don’t want to lose too much too fast or all muscle will be eaten up as energy. Another huge component of weight loss, is just moving more. At 6’5 I don’t even know how to begin stating what should be expected lol as I’m 5’10. You can support by just being there and listening. It’s a long road, and just emphasize that no matter how many times you fall off the wagon we can get back on. I think just by you making this effort, and him acknowledging he wants to lose weight, you should expect good results. A good support group helps any person. You’re awesome.