Spend time with him
Source: https://www.rottentomatoes.com/
Spending time with him can be done in so many ways. You could go to the movies, grab a bite, hang out at the park, or even just sit next to each other and talk. What matters is that you are putting in the time to get to know him. It’s easy to say how you feel but it’s a totally different story to show it. Make him get used to you being around to the point that he himself seeks out for you. Do not smother him though, find the balance where there is room for him to still miss you. Eventually, it will be him showing up wanting to spend time with you even in the silliest ways.