How to move WordPress site to new domain?

Hi,So i am creating a website for a client of mine and i made a test site on my hosting (Hostgator). He really liked the test site and wants me to transfer it to his domain. But he has different hosting than me (Webhostinghub). Also, the test site that i made is a sub-domain (ex. https://www.test.domain.com). Also, I use Godaddy for my domains and he uses a different company (so there are 4 different accounts involved).
How can i move the test site over to his domain?