1. You have until the due date of your 2019 tax return to recharacterize a distribution made to your traditional IRA for 2019 to be a Roth IRA contribution for 2019 instead. (Since you mention your 2019 MAGI as being below the limit for a Roth IRA contribution for 2019, I assume that the contribution made in early 2019 was for 2019, not for 2018).
2. You have until the due date of your 2020 tax return, including extensions, to recharacterize your contribution made for 2020.
Custodians have special forms for requesting a recharacterization. Follow the procedure dictated by the custodian.
