How do I enter backdoor Roth IRA for 2019 & 2020 with combined contribution made on April 2020.

On April 28th 2020, I did my first ever backdoor Roth IRA with one of the investment company. I contributed $6k towards 2019 and another $6k towards 2020, a total of $12k that was received in the traditional IRA and same day was fully converted to Roth IRA. I got 1099-R this year with $12k. I read all the posts but could not find any direction on how to enter both amount for both years. Please hlep!