How to create a data checker/ reviewer role

Welcome to the ODK forum, @Him ! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!

You have looked at Submission review states? https://docs.getodk.org/central-submissions/#submission-review-states

Do you need to restrict it so that each regional reviewer can only see the submissions from their region?

How many devices are being used in each region? Could the regional review step take place on the devices themselves pre-submission?