This will allow you to export your data from Teamleader and modify as needed to fit any custom properties you'll use in HubSpot before importing.
The Zapier looks like it is designed to work the other way, from HubSpot to Teamleader and I didn't see an option for ticket creation in HubSpot.
A couple of suggestions:
1 - run a test import using a smaller export from Teamleader, maybe do 1 month of your oldest tickets and do a smaller test with open tickets.
2 - wait to import your open tickets until your team is ready to start working in HubSpot, importing changes will cause a lot of rework. Use your old tickets to fine-tune the import process and use batches to optimize your data accordingly.