If any form field is deleted accidentally, it can be reverted by using the form XML. Please follow the steps mentioned below to revert the deletion.
Go to the forms list overview page.
Download the XML of the form that you want to undo deleted fields for.
...
The list of deleted fields is available in the exported form XML underneath the <deletedFields> tag.
...
Move the fields from "<deletedFields>" section to "<undoDeletedFields>" which you want to undo.
Import updated XML file from the form list page.
...
