How to send estimated tax for 2020

For July 15 deadline, I'll need to pay the estimated taxes for following two quarters:

First quarter: formerly due on April 15
Second quarter: formerly due on June 15

My question is that should I
1)Fill two separate Payment Voucher forms and write two separate checks, or
2)Fill one Payment Voucher form and write one check (with the sum of two quarters' due)