I need an anonymous form (no names, emails etc) that shows unique ID so that if a person decided to reveal that ID to me I will be able to find his/her answers in the spreadsheet. The ID can show on the form or in the "Thank you" massage after submitting. Like mentioned before - emailing is not an option. I know of similar posts but for this particular problem I haven't found an answer.
Interacting with Google Forms before or during submission is not possible.
You could use the Google Apps Script HTML Service for designing the "Thank you" message page presented after submitting the form (that will carry the ID followed by an explicit message for the submitters to copy down this ID) and create an app to handle your issue.
You could start though by creating a unique ID for your submissions.
Google Forms automatically assigns a unique id to each submitted response once the response is submitted. This id is part of the edit response URL which is displayed on the response submission confirmation page.
Another alternative is to add an optional question to allow respondent to write their own tracking code. You could suggest that write something like a color and a dessert name, or something like that.
To enable the option to allow respondent to edit their answers, from Send your form to respondents
You can choose whether someone can edit a response they’ve already submitted.
- Open a form in Google Forms.
- At the top right, click Settings .
- Check the box next to "Edit after submit."
- Click SAVE.