Help! Needs Sample of Screenshots for Codecanyon Mobile App product

I uploaded a product before and got rejected due to screenshots which i believe i am doing the right screenshots size and ratio.
I am about to submit another product and i dont wana get hard rejection again.
Please i need help on how to go about screenshot size of this product. is there any software/link/site/platform to resize or create for codecanyon requirement?

Kindly suggest me please.