You can import the data from Jira in two ways: straight after registration or later through the Company settings.

In order to import the data after registration, move over to the Start Options page, choose Import > Import from Jira. Insert the web address of your company in Jira, your email address and a password into the pop-up screen.

After pressing the log in button, you will be offered a choice of projects for import. Mark the required projects and click Continue.  

Confirm the import details. If needed, you can remove unnecessary projects from the import list. When everything is ready, you can Start Import.

You can track the import process on the progress bar. The import can also be canceled, but please bear in mind, that all the imported data will be lost.

When the import is complete, you will be notified. The imported project will be available from the left menu.

You can learn how Jira elements are transferred into Hygger from Jira Migration Guide.