There are two ways to assign call priority to contacts.

Upon import:

Before import, add in a column called 'Call Priority' into you CSV file. Import the file but make sure to the Call Priority column is mapped to the VanillaSoft field called Call Priority.

After import, batch update:

Build a Contact Management query of all the contacts you want to assign a call priority to. In this query add in the field Call Priority with no filters. Run the query, go to Perform Task, select Update Contacts. Check the filed, Call Priority and in the Value field enter in the call priority you wish to assign to these contacts. Click Update and wait for the update process to finish. 

Note: It is important to remember that a blank call priority is the highest priority. Priority is then based on a text sort (i.e. 02 comes before 10, but 2 comes after 10). Letters or numbers can be used in the Call Priority field. The highest priority is blank, so leaving certain contacts with a blank Call Priority will give those the highest priority.

It is also important to note that Call Priority works ONLY for uncalled contacts. After a contact has been resulted the routing will be determined by the Result Action of the Result Code given, and NOT the Call Priority.