How do I update a customers contact details?

Hi there, benhiltongranfer

I can guide you on how you can update your customer's contact information in QuickBooks Online

When you editing your customer's data, the changes will appear in other areas of your company's account, which include previously delivered invoices. It also changes any recurring templates that include previously entered information like as billing, shipping, and email addresses, as well as the desired payment method and terms. 

To edit:

1. Go to the Sales menu, then choose Customers.
2. Pick the customer you want to update.
3. Select the Customer Details tab.
4. Click on Edit.
5. Make the necessary changes.
6. Then, hit Save.

You can this article for more information about managing customer lists: Add and manage customers in QuickBooks Online.

I've also added this resource once you're ready to send statements to your customers: Create and send customer statements in QuickBooks Online.

I'll be around if you still need my assistance or have other follow-up questions about managing your customer's data. Just them in the comment section below. Have a great day!