In this documentation, you'll learn how to edit the Order Summary section title.
Here's what we're going to edit:

Follow along:
Step 1: Go to the 'Fields' tab in Checkout
Click the pencil icon on the 'Order Summary' section.

When you do so, a popup shows.
Step 2: Edit the 'Order Summary' title

Change the title as per your requirements.
When you're done, press the 'Update' button.
Step 3: Hit the 'Save changes' button

This will save your changes.
Here's the final output:

This is how you can edit the title of the Order Summary section.