Can I convert a PNG that I’ve already made into an SVG file?
You can trace it in Illustrator and save it as SVG file.
I don’t see a trace feature in the web-app. it would be changing from one format bitmap to another vector. I think besides the Adobe Illustrator, CorelDRAW, Affinity Designer (all paid software), and Inkscape (free to use) have a trace feature, I think there are web-based converters also. I have not used them. Many designers build-in vector format to allow scalability without losing details. You can tell when people have traced a flattened design it often doesn’t cut well or at all.