The Join tool does the opposite to the Cutter tool. It joins pitch blocks together to make pitch tracking and modification coarser with respect to time. It is selected using the contextual menu or by pressing J on the computer keyboard. The cursor appears as the symbol shown, and can be applied (LEFT CLICK) at any junction between two pitch blocks to join them.
The result is just one pitch block as shown in the first picture in the Cutter tool section.
The Join tool can also be dragged across multiple pitch blocks to join them, by holding down the mouse button and dragging across multiple blocks.