i did the same thing! Hopefully someone can answer this. Is there a way to reset the brushes to default other than creating a new project? That's the only solution I've come up with so far but if you are in the middle of a drawing that doesn't really help. You could always copy what you are working on and then paste it as an image in a new project in the photo layer and then change one of your brushes to the background colour and cover what you wanted to earse. But obviously that is not an ideal solution because if you erase what you do your pasted image will be revealed again. If you plan on moving the image over to photoshop eventually that may mess it up Because the transparent layer will be gone.
Anyway hopefully there is an easy way to set your brushes back to default in a project but so far the way I understand it... you can customize your brushes in each project differently but the customized bushes will be used in each new sketch in that project. Really I think this is an awesome feature because it means for my "sketch book" project I can have all my brushes as different levels of gray pencils and I don't need to waste time setting them up each time. But yes I too made the mistake of changing my eraser to a pencil and now I can't change the colour but it always comes out black instead of earsing.
My apologies for this. It's a bug we discovered this past week that was also in Adobe Draw. There's an update for Draw already in the iTunes App store and the update for Sketch is on its way.
I have good news and bad (not super bad) news.
Good: The brush settings are per project. So if you open a new project an eraser will be there.
(Not super) Bad: That doesn't help you with your current project. But we're fixing it and will be updating the app.
Until then, just hang on to that project because when the update is installed it will make it impossible to change the eraser to a brush AND it will put the eraser back into the project where it was changed.
Hope I answered soon enough for you not to worry about it too much.