You don't necessarily want to just ask for volunteers as that's a great way to summon exactly the kind of people you don't want to put in charge of online communities. The best way is usually to notice people who are already part of the community and consistently make positive contributions, then ask for their help. If none of those people want to, though, you're stuck.
Flashback to when the creator of lemmy.world/c/the_pack was looking for mods. I volunteered with
I’m also a shitty mod and will disappear for weeks at a time. I only have experience modding a small subreddit and have no familiarity with Lemmy’s mod tools. Feel free to hit me up.
I passed the vibe check and now I'm exactly as crap a mod as I said I'd be.