Hi there! Have you given a look at this excellent tutorial written by Ashley ? https://www.scirra.com/tutorials/73/sup ... reen-sizes
Depending on the format in which you export your game, several tools are available to you. The best thing I could recommend would be to export it using Cordova, then download the Intel XDK software, and within it, you have a Simulate tab which will allow you to choose different phones and tablets between android and iOs. It will simulate how your game will look on each screen.