1. Go to your Shopify Admin, find "Settings" in the left-hand menu, and click on it.
2. Once you're in, locate the "General" section, scroll down, and you'll see the Order ID option where you can set your Shopify order format.
P.S.
When your Shopify store is synced with JetPrint, your order format will match the External Order ID on the JetPrint order page.