You'll need to submit a ticket:
https://support.fongo.com/hc/en-us/requests/new.
Choose "My Account Inquiry" for the final issue type.
Support staff is under no obligation to respond on these forums. I have no clue what response they'll provide to the ticket either, given the Acceptable Use Policy. Regardless, you'll need to submit a ticket if you want to change your SIP password.
https://www.freephoneline.ca/terms
"Acceptable Use Policy
The Customer may make use of the Services solely for his/her own personal, residential use. The Service is to be used for voice only purposes. The Customer may not resell or transfer the Service to any other person for any purpose, or charge any other person for the use of the Service."