This can be done using a few functions:
testfile = sltest.testmanager.TestFile("test_file.mldatx"); % create new test file
testsuite = sltest.testmanager.TestSuite(testfile,"New Test Suite"); % create new test suite in test file
testcase1 = sltest.testmanager.TestCase(testsuite,'equivalence',"First Equivalence Test Case"); % create a new test case within the test suite
testcase2 = sltest.testmanager.TestCase(testsuite,'equivalence',"Second Equivalence Test Case");% create a second new test case within the same test suite
testCases = getTestCases(testsuite) % list the test cases within that test suite
testCases(1).Description = "First Equivalence Test Case #equivtest"; % create a description for the first test case using a tag
testCases(2).Description = "Second Equivalence Test Case"; % create a description for the second test case without using a tag
testCases = getTestCases(testsuite) % list the test cases again
testCaseDescriptions = string({testCases.Description}); % get the test case descriptions
equivTests = contains(testCaseDescriptions,"#equivtest"); % find only test cases with tag in description
testCases(equivTests) % display test cases with tag
