How do I reconnect with an old friend?

We were friends in elementary and we split up in high school. He asked me to play a game with me a year into high school, I didn’t reply to him because I didn’t play that game anymore and left him on read. He asked me how I was doing about a month later, I replied to him but I didn’t ask how he was doing. I chatted him again to wish him a happy birthday and asked how he was doing, he replied to me in the same way I replied.

I want to know how we can be friends again even if we don’t go to the same school anymore. I’m awkward and shy. We weren’t too close back then but he was fun to play with.