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linking test uit to an existing test case when import from Excel

One answer

Do you mean Test Suite?
There's an existing sample "TestSuite with TestCases 001" with link a new test suite to new test cases.
To link a new test suite to existing test case, you can modify the cfg file like below:
testsuite.XLSArtifactID=C1
testsuite.dc:title=C1
testsuite.dc:description=A4
testsuite.testcase=Link(L1)
In the cell of "L1", you can add the external ids of existing test cases, such as:
urn:com.ibm.rqm:testcase:39
urn:com.ibm.rqm:testcase:40
Please also refer to https://jazz.net/wiki/bin/view/Main/RQMExcelWordImporter for the detail syntax.