How should we edit the Actual result of the test cases which is already executed in test set

Currently, Run History cannot be edited. I.e. once you finish Test or Test Set run, you cannot change its Run Status, Actual Results, etc.

BTW, we have a corresponding feature request: https://community.smartbear.com/t5/QAComplete-Feature-Requests/Add-option-to-edit-test-outcome-for-a-completed-test-run/idc-p/101989#M126

You're welcome to increase its rate by giving it a Kudo.