What you could do is mimic the exact same metamodel in your new project and then simply use the old database. After that you can change whatever you want. Note that you can't use the same database for two different models at the same time, I recommend that you make a copy.

If you don't want to do that you could always create a webservice in your old project which returns all of your data, and then import it in the new project with a call webservice microflow.