How do users gain access to their listing if they posted without being logged in

I have setup my listing directory so users don’t have to sign up to make a posting.

When users create a posting they select that they are the owners. Then how can they modify that listing in the future?

If they visit their listing it shows a check mark showing that is has been claimed. They don’t have a user password to access the account, so they can’t just login and modify the listing because they never created password. So how do they get access to the listing they created?

Thank you.