Not quite sure if you're using Photoshop of Illustrator, but on Illustrator:

1. I'd normally create an Artboard on each elements that I'd want to export as PNG. (Just use the Artboard tool and click the **grouped** elements you'd want to export.)
2. File > Export > Export As...
3. Rename the file
4. Set save as type (PNG)
5. Check the "Use Artboards" and select the number of Artboards you'd want to save or select All.
6. Export.

[![enter image description here][1]][1]

This method will automatically add a "-01" at the end of the file name and will increase the number for each artboard.


  [1]: https://i.sstatic.net/V1D4G.png