Distinct list operation on existing filtered list in microflow

How can i get Distinct list based on one of the attribute. I want to use the filtered list already available in microflow as i am running in a loop and cant use complete database entity as it will affect my performance. I tried to write oql statement but i couldnt find any way to use the existing list instead of complete database table. Please let me know how to achieve this using oql or any other.
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