Kokumin kenko hoken and moving out

Hello!

I moved to Japan mid June and I registered on the city hall and Kokumin kenko hoken, and I plan to move out mid July to another prefecture. How do I pay July's slip?

I'm supposed to receive a letter but so far it hasn't arrived yet. Tomorrow I was planing to give my move out notice to the city hall. Should I wait a little longer? Is there any way to pay each month without waiting for a letter in the mailbox?

Thanks in advance!