Typically, especially in early communities, you just open a public post asking for moderators and come up with some level of criteria for selection. Ask them to submit an “application” through DM or publicly with their previous experience, engagement with the community (for example, if it’s a local community for a town, ask them if they live in the town, how long they have lived there, etc.), and their availability to moderate (1hr a day? Always online? Every couple days?)
In the infancy of a community, it’s more likely you’ll find people who are engaged as hobbyists or passionate about the thing, then as time goes on you run the risk of new applicants being “power hungry”.