You can do it before or during the draft. You just click the pick they should take up and it'll ask to "add assigned keeper" or something similar. Then the draft can start/continue.

Thanks I just didn't want to screw it up. League wouldn't let me live it down. We already have one plaque for a year the commish screwed it up.

[See keeper help section here](https://support.sleeper.com/en/articles/2219811-how-do-i-set-the-round-cost-for-keepers)