You can change the date format of your invoices by following the simple steps below.
Step 1: Open Simple Invoice from your Shopify store’s “Apps” section.
Step 2: Click on the “Templates” on the Simple Invoice dashboard.
Step 3: Click on the “Formats” section, and select the Date Format you wish to print on your invoices from the Date Format dropdown menu.
Step 4: Click on the Save button.