If your admin has enabled Portfolio Forecaster for Jira, you should be able to access it from inside a project.
Once you are in your desired project, you’ll find Portfolio Forecaster in the project’s left navbar.
Good to know
The configurations you make in the Portfolio Forecaster are saved for the current project for your user.
Each user can create and save their own configuration for each project.
Next time you come back to this project it will pull the same configurations you used before.