Your New Customer Offer should be set up during your onboarding; however, you can always make changes to it in your Merchant Center. To do so:
1. Log in to your Merchant Center and navigate to the "Campaigns" tab, choosing "New Customer" from the drop-down menu
2. The first block of text under the infographics will have your default New Customer Offer. Click the purple "Edit Offer" text to the right
3. Make any applicable changes to the expiration timeline, title, offer, tagline, and fine print. Once your edits are complete, scroll to the bottom and click "Save and Close"