Hello there, @ZDOutdoor.

Letting your customers enter their own information is currently not possible. You'll need to manually enter each detail in their profile.

1. Go to the Sales menu.
2. Select Customers.
3. Click the New customer button to add one.
4. Locate and click the name of the customers to update their information.
5. Select the Edit button.
6. Input all necessary details in the Customer information window.
7. Click Save.

You can toggle on the Address, Notes, Tax info, Payment and billing, Language, Attachments, and Additional Info tabs to provide other sorts of information on the customer's account as shown in the screenshot below.

You can also utilize the suggestion of Fiat Lux - ASIA to let your customers enter  their own credit card credentials.

In case you've duplicated a customer's information in the system, you have the option to merge them. This will delete one customer and reassigns all its data to another customer. You can refer to this article for the steps: Manage your customer list. The "Merge customers" section will guide you on how it's done and provides you an important reminder before performing the said process.

To learn a few ways on how to record transactions in QuickBooks Online, here's an article that lays out a detailed information: Record invoice payments.

Please let me know if you have other concerns. I'm just around to help.