Hi There,
You need to export your data into the tar file. See repository export command at
http://publib.boulder.ibm.com/infocenter/clmhelp/v3r0m1/topic/com.ibm.jazz.install.doc/topics/r_repotools_export.html

Afterward exported tar file can be imported using the import command

http://publib.boulder.ibm.com/infocenter/clmhelp/v3r0m1/topic/com.ibm.jazz.install.doc/topics/r_repotools_import.html

However I would suggest you to look at
http://publib.boulder.ibm.com/infocenter/clmhelp/v3r0m1/nav/6_4
to better assess migration scenario at your end. Besides tar files you may also have to copy other configuration files.

Our RQM server will be migrated from CDL to RTP, how to export the existed datum (test cases, test plan) in RQM server and import them to another server? Which tool should I use in this case?

This may not work if you have external references in your data. See the article at https://jazz.net/library/article/686 for details.

- Rob