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 import the risk impact, risk probability, or level of risk. This is because they are held in the system using a special format.
We do have plans to create a full import tool in the future.