First make it known you are thinking to do this and seek feedback on who may be interested.
Take-your-time.
Asking in advance may save you frustration as the level headed ones you’d ask often won’t touch the job, you may be left with those who are indifferent or who are freakishly zealous.
That is frustrating as you’ll see things the indifferent ones aren’t handling as you’d wish and see the zealous ones thinking they’re prison guards, i.e. you will need to moderate the moderators, if you choose wrong they may actually alienate users and harm your forum.
Any visitor who spends time at your forum increases your sites value, you do not want to chase off any users if it can be avoided, moderators may not comprehend or value that, you may not yourself, spend some time learning about bounce rate etc and visitor value.
To understand better check out sites like
https://www.similarweb.com
Also, allowing users to interact with each other in seemingly unhealthy ways may actually be healthy, for them and your board, they will come back for more, if you look at sites like Infowars you’ll see a huge site built on bad vibes, Facebook became big by capitalizing on peoples narcissism, two seemingly undesirable traits that warrant a closer look, if you care of course.
Seek peace maker moderators with tact, patience and a desire to help others, ones who only want to use a ban hammer and get off on a power trip will cost you users, and you never know what value a single user can bring.
My best suggestion is again, take your time, announce it, wait and feel out the feedback, let it sit awhile and revisit, you don’t want to loose good, valuable day to day visitors as they make poor, costly day to day moderators.