What details reveal Gene's guilt over his action toward Finny?In addition, how does Gene try to make amends to Finny for what has occured? This was...

I'm assuming you are referring to Gene's bouncing of the
branch of the tree which causes Finny to fall.

Gene
displays his feelings of guilt in various ways. He dresses in Finny's clothing one
evening and discovers enormous relief in taking refuge in Finny's character for that
period of time. Gene cries when Dr. Stanpole informs him that Finny's days as an athlete
are finished. When Gene is finally allowed to visit Finny in the school infirmary, he
attempts to confess but is unable to make himself say the words until it is too late and
he is ushered out of the room. When Gene visits Finny's home on the way to Devon in the
fall, Gene does confess that he "deliberately jounced the limb so you would fall off"
but then backs away from his statement, explaining "I never sleep much on trains. I
guess I'm not making too much sense today." All these actions are reflections of the
guilty feelings Gene felt in the aftermath of the incident at the
tree.