I am a Graphic Designer, I have designed an app and gave it to the developers, Now they are asking App assets in HDPI, XHDPI, XXHDPI how should i slice them? it should fit perfectly but i dont know the method.
It may be slightly easier to work at mdpi. For asset creation, hdpi is 1.5x those at mdpi, xhdpi is 2x, xxhdpi is 3x. So, for an asset that is 100px square, for example, you'll have assets which are (100px (m), 150px (h), 200px (xh), 300px (xxh)).
If you do need to work at hdpi as your base, create assets for xhdpi that are a third bigger and for xxhdpi that are twice as big.
I'd also suggest reading Google's design guidelines here.
They have some excellent resources here including links to all their icons and helpful sticker sheets.