Push up on the Superba door lever recessed at the top front edge of the appliance to open the dishwasher.
Lower the door and pull out the Superba's bottom rack to locate the screen cover inside the bottom. The cover has a series of holes and a plastic lip sticking upward. Rotate the bottom sprayer arm if necessary to get it out of the way so you can locate the screen.
Grab the plastic lip and twist 1/2 turn to the left to disengage the screen and remove the part.
Reach inside the compartment below the screen to remove the filter cartridge, which you can clean under running water and re-install or replace with a new filter. These are available at appliance repair shops.