In each questionnaire, you can enable the respondent to edit his answers.
In the 'EDIT' - 'Settings' - 'Respondent access' tab, you can enable the respondent who has already filled in your survey by turning the cookies on, so that he can then edit his answers when he has re-clicked on the survey, but this means that the data and analyses have changed, so it's mostly (but not always) better to indicate that he cannot edit his answers.
Use of URL address
In the 'EDIT' - 'Questionnaire' tab, you can turn on the 'Show link for later editing' option at the end. When the respondent comes to the end of the survey, the URL will be printed out, through which he will be able to access the survey later and edit his answers.
Use of identification codes
You can enable an individualized invitation in the 'PUBLISH' - 'Invitations' tab. In the email invitation settings, you can choose between automatic and manual entry of an individual code. In the tab 'EDIT' - 'Settings' - 'Respondent access' you can then change the cookie settings and check the option "can edit responses later". 1KA invitation sending system is available in the 3KA private package.