If he's food motivated use grain in a bucket and treats. Be careful not to spoil him but it can help with nervous horses if used properly.
Realax and be chill, horses tend to pick up bad vibes. Also have just one on one bonding time together and make sure you show lots of love and support!
This is what I do but I recommend just spending time with them. Such as grazing for awile, Sitting in or out of the stall, or going out it the field and just watching them.