Click on your checkout page > Hit the pencil icon appearing beside the name of your page.
When you do so, a popup window shows up.
Insert a name that you want to have for the selected checkout page.
You can even change the permalink of this page.
Once done, click on the ‘Update’ button. It'll change the name and URL of your checkout page.
That's it! This is how you can rename the name and permalink of your checkout page.