After successfully cloning my repo from heroku and added another remote
1/ git clone git@heroku.com:[APP].git
2/ git remote add bitbucket ssh://git@bitbucket
Steps:
Create ssh keys on source server
ssh-keygen
Cat and copy id_rsa.pub located under ~./ssh directory
Check if it works by running below command on the source server
git remote show origin
For fetch and push from the source server, if the protocol is 'https' then you have to change it to 'git+ssh' by running below command
git remote set-url origin git+ssh://
Check if you can do push to the repo.
Done!