You have to go to the manager tab. Open the Project Space where your project is located. When you find the Project you want to migrate you need to click on the arrow next to the project name and select the migrate option. you will have to choose to which environment and which project space in that environment you want to migrate. Once you select that the next window will appear where you need to select what asset you want to migrate (Files, Accounts, Tasks, Pipelines).
If you select the pipeline option all of the pipelines will be migrated to the environment you chose.
NOTE! - You cannot specify individual pipelines for migration using the Migrate option. You will have to use the import and export functionality for a single/multiple pipelines.