The easiest way to move a Project between Story Workflows is to do so when you are creating the new Story Workflow. The newly created Story Workflow will "inherit" the Workflow of the Project, and once the Story Workflow is created, you can then customize your Workflow as needed.
More on this - Article: Creating and Editing Story Workflows.
If you have already created a Story Workflow and now want to move over a Project or even two or three, you can do so by navigating to Settings > Story Workflows and clicking on the Story Workflow that contains the Project you'd like to move.
Then you can click on the Project and select the Story Workflow you'd like to move it over to.
In the case that you want to move a Project to another Story Workflow that has a different Workflow, you can update Story Workflow 2's Workflow to match the Workflow of Story Workflow 1.