Lol okay i have ibispaint but im bad at shading so I'll just try xd
XD I also have Ibispaintx
I think I can help you shade!(just be good at remembering lol)
1. Add a layer
2. Choose black or dark purple
3. Cover the top of the eye(It's a bit confusing because I'm not able to send a video of a tutorial) and go lightly with the brush