The Checkout lets you use the customers' shipping address as the billing address by default.
Follow the steps below to set it up:
Step 1: Go to the 'Fields' tab
Drag and drop the "Billing Address" fields ahead of the "Shipping Address" fields.
Step 2: Rearrange the address fields
Step 3: Enable the option to enter a different shipping address
Click on the 'Shipping Address' field.
Scroll down to the bottom of the list.
Click on the eye icon beside the option - 'Use a different shipping address'.
Next, click on the 'Update' button.
Step 4: Click on the "Save changes" button
This will update the changes.
This is how you can set up the form with billing details instead of shipping details.