I edited a PPT but it saved as Google file. How do I get PPT back?

I assume PPT means PowerPoint. What I understand you said is that you exported your powerpoint to your google account, meaning your google drive. If you go to your google drive, which can be located at drive.google.com , you will see the files which are saved on your account. Click on the appropriate document, wait for it to open up, then click the "File" tab and scroll down to "Download As". In "Download As", you can click on Microsoft PowerPoint in order to get a PPT again.
If, however, by "Google File", you mean it was a file which you downloaded off of Google and edited, the file could be found in "File Explorer" on your computer under the tab "Downloads". Message me if you need additional help.