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To save and reuse the Project Plan, you can create a Plan template and export it in the form of an xml file with the option provided for Export Plan in Plan module.
You can store this xml file on your machine and import it later whenever you create new projects.
I am providing you a link which explains how to import or export a plan from Plan module:
Please refer the above link.
If you are still facing any issues, Please feel free to contact us. We are happy to help you.