From an existing Bugzilla

If you have an existing Bugzilla you’d like to move to devZing we are happy to do that at no additional charge. We’ll even do it more than once to give you a chance to try us out with your data without having to commit. Please contact support and we’ll let you know how to get a backup of your current Bugzilla and get it over to us.

From a different bug tracker

There isn’t a straightforward way to import bugs into Bugzilla from another bug tracking system or from a spreadsheet. That said, we’ve developed a number of internal tools to assist with migrating your data into Bugzilla. Please contact support to discuss what might be appropriate for your situation.