During boot / load game:

Hold the [TAB] button pressed and a menu with extra settings appears.

While playing:

Set game in pause mode (by means of the MSX [STOP] key).
Then type "help me" (without quotes)
You hear a sound effect if it went well.
Now you can with the keys [0], [1], [2], [3], [4] and [5] assign yourself vitality and items.
Press [STOP] again to continue playing.