Assign test executions based on Assignee in test case definition

Hi,
Could you please advise how to do bulk assign of test executions to assignees of test case definitions?
I have imported test cases from excel, I see correct assignees in the test case definitions, however those assignees are not populated to the test cases executions. I have more than 3k test cases and more than 150 users, manual assignment is very time consuming.
Rg,
Pawel