You can find option here:
To turn on training mode, you need to start VS mode first. After starting the round, you need to press "F" on BOTH 1P and 2P control once to activate training mode.
Please note: "F" is not the one on your keyboard, it's the game's input. So you need to bind it with a key first
Also, remember to set round timer to "0" if you want infinite time for training:
