How to add a custom Meta tag to Yoast

Hi.
I’ve read all previous topics about disabling “meta keyword” from Yoast.
It’s not a professional move to removing this option just because you think so. what about those old members of yoast which think Meta keyword is necessary ? please bring it back optional.

Or just help me to add it manually: I can use “Custom fields” for this (add my keywords in a custom field and show it in header).

so how can I add this custom field into the yoast meta tags? just because I’m obsessive I would rather to be clear and tidy and showing meta keyword right after meta description.

Can you help me with this?
by the way I bought a premium version of Yoast should I ticket this on yoast panel?