If you want to move a layer in Magma, or just a piece of it to another part of the canvas, then You can use the Move tool. The shortcut for this on your keyboard is V.

By default the active selection for the Move tool is the entire layer you are currently working on. Use the Move tool to click and drag it across to a different part of your canvas.

To move only a portion of your layer, first use one of your selection tools (Selection, Circle Selection, or Lasso Selection) to outline the area. Then switch to your Move tool. Click and drag your selection to its new location.

To move your selection along a horizontal or vertical axis, press and hold SHIFT, then click and drag left or right, or up or down. Your object will move along a straight line to its new point.

If you have a part of your drawing on a separate layer, but can't figure out which layer it is, use the Move tool together with Ctrl.

Press and hold Ctrl and then click on the part of your drawing you want to find the layer for. After clicking, that layer will become your active one.