How to transform a certain part of a drawing

(I made a thread asking about this before but every time I try and check it gives me an error for some reason)

So I need help with something, I’m trying to select and transform a part of a drawing on a bitmap drawing layer but every time I use the select tool and try to select a part of the drawing it selects the whole thing. I’ve looked around in the settings and I can’t find anything that would fix this.

If the bitmap is on the same layer I think it will select the whole drawing every time. its not like in a vector layer where you can select a few lines .
So If you want to change just a part I think you need to use the cutter to cut that part out and best is to move it to a separate layer if you want to be flexible.
Its not like in Photoshop that you can select a part abd then adjust it, even if that would be great if you could.