Someone else created these steps, but it worked for me
"1. Logged in with GC Key account.
2. Permanent Residence > Family Class (Spouses)
2. Application Number and Family Name - Copy/pasted application number from email (including the F) and entered PA's last name. If you don't have App Number, use Family Name, Birthday, Place of Birth
3. City of Birth - I entered 1 space (hit spacebar once)
4. Country of Birth - Selected PA's country of birth
5. Passport Info - Did not enter any passport info
6. Other Application Info - Filled out the other application info as per our application and put '2' as the number of members in the application."
Always use the Principal Applicant's info.
If this doesn't work, there are so many threads in this forum that can help you
Good luck