After some use, the rubber feet at the bottom of the keyboard can gather dirt and dust (depending on how dirty your desk is).
To clean them, you need to remove the feet completely.
Then, clean the adhesive on the feet with a plastic scraper.
If you don't have a plastic scraper, you can use a BIC pen cap or any other plastic object to avoid damaging the keyboard base.
Then clean the keyboard's base with alcohol.
To put them back into place, use 3M double-sided tape or some kind of strong glue, preferably contact or AB glue.
Do not use Loctite or superglue, as these can damage the base and the keyboard's mylar material.
If you use double-sided tape, make sure the tape follows the shape of the rubber feet. Be careful when doing this. Also, be careful not to stain the bottom mylar sticker or damage the rubber feet.