Hi Angelina,
If you have not committed your change yet.
Simply download the latest version of your app from team server.
If you don’t have a lot of changes you could also revert the entire project from the project directory using SVN (if you’re familiar with it).
https://docs.mendix.com/refguide/version-control
Alternatively, if you’ve already made too many changes and don’t want to lose on that, you could download the latest version of the project and copy the page to your working project. Note that you may have to change the name of the existing project (as Mx remembers that you already have that project on your local machine)
However, if the page was built newly and never committed, there is no way to retrieve that and you will have to create it again.