To use your Blackberry contacts with Covve you can export them from your Blackberry and import them into the address book that you have linked with Covve (gMail or Outlook). These will then synchronize with Covve.
This article from PCAdvisor sets out the steps for extracting your contacts from a Blackberry to your computer. You can then import them into the Gmail, Outlook or Exchange account that you have linked with Covve.
Instructions on how to import your contacts can be found:
a) Here for Gmail
b) Here for Exchange/Outlook
c) Here for Office365