You may allow your form users to save their submission before sending it and resume it later They will receive a link to the form which they may use to complete their submission. To activate this feature, go to the Settings → Advanced section of your form and select the option Allow respondents to save the submission and resume later.
A new button will show up at the bottom of your form: Save for later. When clicking it, users will be given a link and instructions for using it. When accessing the link, users will see the form with the content they have already filled out. They simply need to continue filling out the form and click either Save for later either Send.
In the Submissions table you will notice a new column called Status. There you will be informed which entry is finished or incomplete.