I've had two shingles shots: Zostavax and Shingrix. There's no reason you couldn't take either shot again. You might have to pay but no big deal.

I know people who've had shingles and it is not only a major PITA but can be life-threatening, can blind you, etc., just bad stuff. Don't delay taking advised precautions, including injections.

So far as I know there's no standard booster protocol for Shingrix.