There are DIP switches on the fail-safe modules ET 200S and ET 200pro for setting the addresses. Here the smallest possible address switch was chosen for the sake of saving space. This makes it sensitive to great pressure and sharp objects. So you should use an appropriate tool to manipulate the address switch.
There are various tools that are commercially available like the DIPSTICK from Grayhill or similar tools which are suitable for manipulating the address switch. You can also use a ballpoint pen if you are careful. In all cases you must exclude the occurrence of burr which would prevent the address switch from being placed in its end position. For this reason you should not use a screwdriver or knife for manipulating the address switch!