First, you need to unlock the option to do so. To do so, you'll need to complete the dialogue with Ori, who will invite you to the lake. Then, accept it and continue with that event, almost at the end you will be able to do it with most of the spirits.
The opportunity will usually arise when you have already declared your love for Ori, or Ori has done so before you. Then you have to have enough hearts for the dialogue to come out.
