Pronouns in japanese songs are always so complicated - when is it "I" ? when is it "you" ? I struggle so much with this so I understand what you're going through lmao --- for example I wonder if the first verse of the song shouldn't be something in the lines of "Your wishes at the tip of my fingers as I shake them" or more literaly "A pinch of my fingers, your wishes"

And so it is absolutely needed to pay close attention to the context - here it seems to be a magician wanting to fulfill "君 (you)"'s wishes as they want "you" to be good.

In the verse "あの子に好かれたら　時を戻せたら", and like in most lines/japanese songs (or anything that is japanese for that matter), the subject is left out in the sentence - but it's here and we "know" it thanks to the context -> a magician wanting the best for "You" + "You" is depicted as the subject in the first verse of the paragraph. ("***君は*** また真面目な顔して傷付くんだ") I guess the meaning of the line is showing regret : "Ah, if I could go back in time and have[make] her love me, then---" but since there is no indication someone's speaking, and from the sole context we have, we can only assume the magician's talking for "You" and so that makes a second person's sentence.

As for the "風呂の床に流すあの日"... honestly this one is hard on me too. I can't get the meaning behind 流す ; what is shedding ? I guess it is vague on purpose but that makes translating it in french really hard for me - and even in english I see the difficulty. Since there is "僕の祈" just after and we know the link between the magician (僕) and "You", and this line is much sooner than when "she" is metionned, I think "You" is a safe bet although that is all about interpretation I guess :0

And no worries! I know Japanese can get really tricky, especially Reol's lyrics. I'm also still learning and that's always better to help each other through this!!