All lesson horses are tuned out to some extent or another. Not (necessarily!) in a bad way, but you're just another person to them.
Do something no one else does. Are you familiar with horses? Maybe taking him out to graze on the lead. Spending some extra time grooming and really groom him, don't just do a quick cleaning.
Of course he will love a treat but I'm sure he gets a TON of treats, it won't make you special.
Be there *for him* be very quiet-just calm and enjoyable to be around, personality not noise (though quiet noise is good too lol). Go nice and slow and do little extra things. If you appeciate him he will start to appreciate you. Rocky has a good post. I'm sure he'd love a good scratch, some are very itchy :)
Make sure you check with the help before doing anything of course. I would not do treats personally.
I worked at a lesson barn for years. You could tell the people who "knew horses" even if they had never been around them before. I would take a person like that over most experienced people any day!! I was always happy to help with "extras" but sometimes wasn't able to and had to say no, so if unclear ask "if you're busy maybe next time? or is this a barn rule". (If you want to handgraze you will be supervised at least at first) The fact that you're even asking brings a smile to my face and tells me you'll be just fine. Ask the help what that horse likes and tell them you want him to feel appreciated. Keep in mind you may not have the horse every lesson and that's just fine.
There was a very nice teenager who made sure to spend time with her horse and wanted to know if he liked her. Honest? He didn't care. She may have spent time with him but her focus wasn't on him. The horse will know what you are paying attention to and what you're trying to do.