Use any hex editor apps that are available for android/iOS and change the value of HEX Dword to any amount you want.
Gems HEX a5 5d 53 fb Dword
If the codes doesn't work, it is possible that your android version is not compatible with the code I provided above.
Fortunately you can do it manually! To do it manually, just use search function in your hex editor app, enter your current Gems value in Forsaken World Mo and search for it (choose DWORD) .
If you see a small list of results, example 10. Just edit the value of them one by one until you can find the real HEX!
If you see a large list of result, you need to change the value of your current Gems value by either using/consuming or adding it. Go back to the list and find your new current Gems value in Forsaken World Mo to the large list and you can now edit the value any amount you want.