> I have no bracket for #3 and #4 slot.
There do exist empty cases that are the size of a 2.5-inch disk-drive, and the hardware inside the case to connect an M.2 device. The case has "standard" SATA "power" and "data" cables. So, put the M.2 into the case, close the case, and mount the case in a 2.5-inch-to-3.5-inch metal bracket, and put the bracket into an empty 3.5 inch slot in your computer's case.