You can use the Save As function to save and name your diagram as a new one to the existing page in Confluence or to a new page.
Start by clicking Edit on an existing named diagram from a Confluence page.
Once the diagram is open, go to File->Save As.
This will open the Save As modal. You can change the name of your new diagram at the top. If you want to save this to the existing page you are on, select This Page.
If you select New Page, you can create and name a new page in Confluence and also save your diagram there right from the modal. Type in the name of your new page name and select the space you want it in.
If you do not see the space you need on the dropdown menu, use your keyvoard to delete the text and as you type it will search through your spaces.
Lastly, you can search for an existing page to save your diagram to.
If you do not see the page you want, you can use the search bar to type and search for a space.
Once you choose the page and space you want to save to, select it and it will highlight blue. Click Save.
After you save, it will refresh the screen and place you into the new copy of your diagram. It will then confirm in green a temporary message that lists the name of your diagram and the page and space it was saved to.