Yes, good question. Unfortunately, Greet is somehow in its own world, and while applying a life cycle approach, the Greet tool uses an own database that (I think) is inaccessible from the outside. There is the Greet excel model, but this has a quite complicated structure and cannot be easily read and imported.
If your question is about how to use openLCA in general, please check the resources in openLCA.org, and also the openLCA youtube channel (
https://www.youtube.com/channel/UCGiahq1YZWK4pRXDVXuIi6w).