In edit mode, you can hoover over a piece and press L key to select it. Or select a vertex and press Ctrl L to select all linked geometry (it can be limited by seams, or materials, or others options, in the black little window that appears in the bottom left of the 3D view, called "Adjust last operation").

In case of more difficult situations you can assign some vertices to a vertex group, that you can later select and deselect when needed).

In edit mode, you can hoover over a piece and press L key to select it. Or select a vertex and press Ctrl L to select all linked geometry (it can be limited by seams, or materials, or others options, in the black little window that appears in the bottom left of the 3D view, called "Adjust last operation").

In case of more difficult situations you can select some vertices and press Ctrl G to assign them to a vertex group, that you can later select and deselect when needed).