How to filter out the converted leads?

Hi everyone, my project is about to remarket the people who submitted a lead form on Facebook, but not converted yet. I have already synced the leads from Facebook to Klaviyo, and then I want to set up an automotive email flow to them from time to time till they converted.

The flow is that:

#1 email - send out right after they submitted a lead form on Facebook

#2 email - send out 7 days after email#1 to those who have submitted a lead form from Facebook but NOT converted yet

#3 email - send out 7 days after email#2 to those who have submitted a lead form from Facebook but NOT converted yet

However, I am not sure how to filter out the converted leads in the #2 and #3 email. It is not reasonable to send them the remarketing emails if they have already converted.

What is the trigger for the filtration? 

Thank you!