We do not currently have a good way of importing risks into Risk Register. You * can * import the risk title and other attributes using the standard Jira import tool:
https://confluence.atlassian.com/adminjiraserver/importing-data-from-csv-938847533.html
However, you cannot do not import the inherent or residual level of risk. This is because they are held in the system using an integer value that is unique to the risk model for your project. We do have plans to create a full import tool in the futureThe system will calculate this based on the risk probability and impacts that you supply.