Going to the Advanced tab (1) of Form Workflow will give you some more options.
=> In order to enable "Send back to requestor" functionality, complete first the Requestor Email box, then tick "Allow Send back to requestor"
=> Tick "Allow on Hold" to authorize reviewers to put requests on hold
=> Tick "Active mobile validation" to enable:
- validation from the reviewers Email mobile App
- as well as validation from a Microsoft mail client / webApp
Check this post for more details
Select the Sheet column containing the requestor(s) email address, in order to enable "Send back to requestor" functionality in response settings.
Click on + (2) to personalize your email template.
Choose from the available fields list to personalize your template.