Since you received a 2019 Form 1099-R, presumably the deposit (contribution) and distribution both occurred in 2019. Since it was an unintended contribution, if the contribution was made on or before April 15, 2019 I assume that you did not specify that it was to be a contribution for 2018. (Let us know if that assumption is wrong).
Was this contribution an excess contribution either because you did not have sufficient compensation to support the contribution, you had already made a contribution for 2019 and when combined with this $6,000 contribution you exceeded the contribution limit, or because you were age 70½ or over in 2019?
What is the code in box 7 of the Form 1099-R?
Is the IRA/SEP/SIMPLE box marked?
