I also draw on an iPad. I either name the file manually in my drawing app before export (I use Procreate/Art Set for drawings, and Pixaki for pixel art), or if you export your drawing to Files instead of to pictures, you can open the Files app, browse to wherever you exported and tap and hold to rename it that way before upload. Or the other thing I do is email it to myself so I can rename and store it on my PC before upload. Some people also draw by hand on paper and then snap a pic on the phone. Whatever works best for you, really!