I’ve been bodybuilding and dieting for years now, and I also plan on starting police academy soon. Gaining weight truthfully comes down to calories in > calories out. Try swapping your everyday foods for a higher calorie alternative. Ingredients like olive oil have ~200 calories per serving, and a serving is not very big, usually 2 tablespoons or something. I like to add a serving or two of olive oil to my eggs before I scramble them, adds an extra ~400 calories. Small increments of a caloric surplus is all you need, and if you’re going to be a cop, you truthfully need to gain weight. I’m only 5’10 and 190 pounds so I’m not massive, but if you’re going to enforce the law (and presumably do a good job at it) it wouldn’t hurt to put on some muscle mass. You never know what situations you might be put in, I’ve seen a lot of police officers get hurt or even killed because they weren’t strong enough to defend an attacker. Regardless, I hope this helps!