The following are examples from the detailed instruction manual included with the plans

When the cabinet has dried and the clamps are removed you can install the Machine Top

 Place the Machine Top face down,  lift the cabinet and set it upside down on top of the Machine Top.

 (Remember that the power connector hole (the larger notch of the machine cutout) needs to be on the right side when sewing.)

 Center the cabinet on the Machine Top, now screw the cabinet to the Machine Top using the pre drilled holes in the corner supports. 

(Do not use any glue just the screws to hold the Machine Top on.) 

Examples of pictures included in the instruction portion of the plans  select the picture to enlarge it for more detail.