Welcome to the Asana Community Forum!
This post is older but I have also seen it in others that many used Unito to perform the initial transition: Automatic migration from Jira to Asana - #3 by Marc
Here is more info from Asana: Jira Cloud + Asana • Asana
Here is another tool that could be used.
And two more listed below in the other thread.
I hope that helps!