With the payment-check-counter advanced setting, you can set the beginning check number that will be assigned when you have a check to export that has a Check Number value of auto_assign.
This setting requires you to type a number in the Setting Value box that indicates the starting number exported checks will be numbered with.
By default, payment-check-counter is set to 0, so exported checks will be numbered sequentially starting with 0.
Changing the default
To change the default, navigate to Settings > Advanced and search for payment-check-counter. Change the Setting Value to the starting number you want checks to be numbered with.