Follow these steps to change the difficulty level for offline mode:
1. Open the Minesweeper.World app.
2. Open the "Game Settings" (gear in the upper right corner)
3. Tap on the button to the right of the "Difficulty" option
4. Choose between "Beginner", "Intermediate", "Advanced", "Expert" and "Custom"
With the Custom option you can also customize the game board to your liking. To adjust the board, drag the bars to the desired position or tap the individual numbers and enter the desired value with the keyboard. The maxium size of a custom board in Minesweeper.World is 99x99 with up to 999 mines.