In the "curve" view you can select a range of points and scale or lift up/down - can you rotate/skew as well?

I have a clip I purchased, but I am trying to create a walk loop from part of the clip. Unfortunately there is some other body movement going on in the clip (a head turn). I copied the last value of the clip and pasted it at the start - you can see where green line is the values are different - they jump quite a lot. I don't want to lose the subtle movements in the clip, but I want to adjust the points to get a smooth movement.

E.g. I would like to grab the blue vertical line on the left edge and drag it upwards, with the right edge not moving. That would adjust all the values in between by an amount proportional to where it is in the clip. It is kinda like rotating the blue box, but it might be more accurately skewing the box. The horizontal blue lines would be on a slight angle. (At the moment you can only move the vertical blue lines left/right for adjusting the length.)

My goal is to keep the subtle value adjustments in the clip, but make it end with the same value that it starts with so I can loop it.

I can scale the box (grab the top edge and drag it down), but that loses all subtle values movements in between. I tried deleting points than manually adjusting them (took too long adjusting them all), which is my last resort.

Is there another way to do this instead?