If tax was withheld on the returned contribution then that would be in box 4 on the 1099-R with the code P. You would also enter that into your 2020 tax return. The box 1 amount will be ignored in 2020 but the box 4 tax withholding will be added to all other W-2 and 1999 withholding.
Tax withheld on a return of excess deferrals is a really bad idea since the excess must be reported and taxed in the year the excess was made but the withholding applies to the tax year that the withholding was done.
The only time that would all be on one 1099-R is when the excess deferral and the return of excess is all in the same tax year, then only one 1099-R is issued with a code 8 for that that year. A code P always means that the excess occurred in the previous tax year.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
