I would suggest you the tip below or/if your .pptx file can't be restored after using it, then use https://onlinefilerepair.com/en/powerpoint-repair-... PowerPoint repair online
• Try importing the slides from the PPTX file rather than actually opening it. Click "Insert," then "Slides From Files." Browse to and select your file, then click "Insert All." This might extract the slides from the corrupted file and place them in a fresh file, though the formatting may be lost. Checking the "Keep source formatting" box might help.
• Try opening the presentation in Word. Open Word and click "Open" in the "File" menu. Use the "Files of type" drop-down menu to select "Recover Text From Any File," then try to open your corrupted PowerPoint file. Again, most of your formatting will probably be lost, but your data will be there.
• Check for a TMP file. These are temporary copies of recently accessed files. There may or may not be a temporary copy of the file you want, but it's worth a shot. Right-click the "Start" button, then click "Search," and run a search for "*.TMP."
The search will return many files, most of them probably with incomprehensible names. Click the "Date Modified" button to sort them according to the last time they were edited and find a file that was created around the time you lost the PowerPoint file. Try to open this in PowerPoint.
• Try opening the file in a different application that supports the PPTX format. The most prominent of these is the Impress program in the OpenOffice suite, a free, open-source alternative to Microsoft Office