After assigning custom fields and tags to your test cases, you can search test cases in the test case list by filtering custom fields and tags.
Go to Test Management > Test Cases.
From the Test Case page, click the filter icon on the Search test case bar.
Within the filter list, navigate to Custom Fields and Tags. Select from the dropdown list below each of them the custom fields and tags based on which you want to query your test case. Click Apply and search to search for test cases with selected custom fields and tags.
Your search result displays all test cases with selected custom fields and tags.