Talk to the 401(k) plan trustee about returning the excess plus any earnings. They will issue a 1099-R showing the return that you will use to file your 2019 tax return.
For information see IRS Pub 525 page 10
https://www.irs.gov/pub/irs-pdf/p525.pdf
Note that this is a 2018 pub so it refers to the 2018 tax year - just adjust the years for 2019.
**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.**
