This feature is available in Ultimate edition only.
Regression tests are grouped under regression suites. You can assign new tests to a suite, or unassign existing tests.
Go to Release Planning > Regression Planning.
From the Plan Type list on the left, click on the suite for which you want to add or remove regression tests. The Summary window opens for the selected suite.
To assign a new regression test to the suite, click Assign Tests and select a test from the drop-down list, then click Assign to move it under the selected regression suite.
To unassign an existing regression test, expand the Regression Test subsection by clicking on the plus sign (+). Select a test from the expanded list and click Unassign to remove it from the selected regression suite.