I know that if you shake it it deletes everything but I made a mistake a long time ago and I want to fix it but there is no eraser.
I completely understand what you are saying.
You've done a sketch, but want to delete a portion, but it is not the last item that you drew. The current system doesn't work because it's an all or last one erase function.
I am planning on sending some constructive feedback on a few apps that's I've downloaded.