Renounce

Less than 1 year here on FLR visa,  is there anything special I need to do to turn in visa when I return to states?  I don't want to continue to be liable for any taxes after I settle up for my time here.

If you are returning to live in the US, you don't do anything. You just get on a plane and fly back.

Unlike the US, you are only liable to pay UK taxes while you are living and working in the UK. As soon as you leave the UK to live abroad, you cease to have any tax obligations to the UK. I believe the US is the only country in the world that taxes people based on citizenship and not residency.

(Not quite sure why you have called the topic 'Renounce' though, because renouncing is when you give up your citizenship)

If you have been working in the UK you may have paid too much tax as the PAYE system will have assumed you would work the full year.

In which case you can file form P85 to let HMRC know you have left the country.

https://www.gov.uk/tax-right-retire-abroad-return-to-uk