When you are not sure what descaling routine you should use, you can always find the correct instructions in the user manual. Please keep in mind that not all garment steamers have a descaling function.
If you do not have the user manual anymore, please try to find your appliance model number on your steamer (should look like GCXXX). Knowing this number, you can find all the product information on the Philips website. If you have any questions, please always feel free to contact Philips Consumer Care