To get a soft idli batter, you will need to use the right type of rice and lentils, and grind them to a smooth and fluffy consistency using a wet grinder or a blender. You will also need to pay attention to the consistency of the batter and add enough water to get a smooth and pourable consistency. Finally, be sure to allow the batter to ferment for the correct amount of time in a warm place to help it rise and become fluffy.