You can either hit Prestige straight away or go to the Progression tab in the Barracks through the Multiplayer lobby. Think carefully about when you want to do this, as Prestige in Black Ops 6 means you lose access to a lot of the things you will have unlocked.

Black Ops 6 player reaches Prestige 1 without getting a single kill in almost twenty hours' worth of multiplayer matches.

If you’re about to prestige in Black Ops 6, you might want to think twice as it has huge stakes in ways you might not think.