Anil, there are some limitations on work item export and import. You will not be able to copy all the information AFAIK. I think you will lose history, approvals, attachments and links. Here are some documents which should help:

I will assume you are using RTC 6.0.3. The steps should be similar if you are on a different version.

Exporting work items
https://www.ibm.com/support/knowledgecenter/en/SSCP65_6.0.3/com.ibm.team.workitem.doc/topics/t_exporting_work_items.html

Copying work items between repositories using CSV export and import
https://jazz.net/library/article/522

Here are some links:

[CCM] Move a project area between repositories                         
https://jazz.net/forum/questions/38129/how-to-move-a-project-area-to-another-rtc-server                                                        
                                                                       
Project move from one server to a new one                              
https://jazz.net/forum/questions/180922/project-move-from-one-server-to-a-new-one                                                              
                                                                       
Is it possible to move workitems from one Project Area (on server A) to
another Project Area (on server b)                                     
https://jazz.net/forum/questions/134174/is-it-possible-to-move-workitems-from-one-project-area-on-server-a-to-another-project-area-on-server-b

If both servers are in the same repository, you can copy a workitem from one project area to the other without loss, however, I believe you can only copy one work item at a time. Open the workitem and select the option to copy or move to a different project area.

https://jazz.net/jazz/web/projects/Rational%20Team%20Concert%20%28SAFe%29#action=com.ibm.team.workitem.viewWorkItem&id=169824

You can copy widgets over from one dashboard to another, but otherwise you need to recreate the dashboards too.
https://www.ibm.com/support/knowledgecenter/en/SSCP65_6.0.3/com.ibm.jazz.dashboard.doc/topics/t_move_viewlet.html

Maybe this is a start.