Resistance level on the app training

Hello everyone, 

i just bought a Boost Bundle tacx and i do not understand how the resistance level works on the training plans the app offers because it is written to keep the level on 2 when using the app but if there is a hill and i keep the level on 2 how should i feel the climb? and if a should change the resistance level how should i know which harder level to put in order to match the difficulty of the climb? thank all