How can I create prepaid orders customer group?

Hello Team,

I am having online shopify store and this is my store URL : https://jhakhasethnics.myshopify.com/

I want to know how can I create a group in my store for customer who have placed an prepaid order or if I can perform some filtering to get the expected result of prepaid order customers. I want to send emails to prepaid order or I want to offer them a special discount for I need a list from where I can specifically target those customers.

Please guide me the best way.

Thanks you
Khushboo