I know this is an old thread but this may help someone else who is looking for the same thing. Go into Layer Manager and right click the layer you're looking for (which is hiding in a block(s)), select Isolate Layers. This takes a few seconds, all the layers in Layer Manager (except the layer you isolate) will be turned off and in Model Space your offending layer will be the only one visible. Then you can click on it and go into Block Editor and change the layer prop to 0 or whatever you want (when you're in Block Editor and change the layer it will warn you that the layer is off or frozen--that's okay, just do it and close the Block Editor and save changes). Then, simply restore all the layers in Layer Manager (or the Layer State if you're using layer states), delete the offending layer and you're done.