reminder notification for the Guest user

Hello,
I created an assignment flow where a decision’s internal user to fill out a form and send this form to a person as an assignment. So, the person that is a Guest user should fill out his own part on the form and can see the internal user’s inputs as well. Also, I need a reminder to remind assignment to the person that is Guest account.
To send the assignment to the Guest user I am using “AssignToGuest” assignment type but as you know this type does not have the reminder notification.
I was looking to [url=https://support.decisions.com/forum/topic1395-email-tasking--email-assignments.aspx]Email Tasking / Email Assignments - Flows - Decisions Forum[/url] question on the forum that is helpful but here the assignment type is “Assigned”
Can you give me an idea how to build a reminder notification for the Guest user?
Thanks
John Balta