Modify generated Pass Templates (Menu->Templates->Pass Templates). These templates are used in Apple Pay and Google Pay campaigns. After modification, activate the templates.
Alternately, you can create your own templates and select them in your campaigns.
Modify pass download campaigns
Modify generated Apple Pay/Google Pay campaigns (CampaignId starting with welcome_pass) to customize your message and instructions on passes. (Menu->Campaigns->Apple Pay or Menu->Campaigns->Google Pay). Activate campaigns.
You can use Preview from the campaign page to check how your pass would look.
Update passes using campaigns
Use subsequent Apple Pay/Google Pay campaigns to notify customers who have downloaded passes with your promotional message with image. Passes in Apple Pay and Google Pay provide Geo-fenced targeting around your business locations.