I think you have cloned the upstream repo where you do not have write access. You are supposed to fork this repo into your account, clone your fork locally, make changes in your local clone, push it back to your fork, and create pull request to this repo. This is the process of how you contribute to the project. To resolve this, please fork the repo into your account and then clone the forked repo and work on it and push it back to the forked repo then you can ask your organization for push and pull requests.
If you are constantly working with Git then you would like to know more about these frequently used git commands. Also, you can join the Git training offered by Intellipaat.