I have the same frother as in the image and just downloaded and printed the STL but the lid is way too small. When I put it on the original lid you can see that the inner portion that should be snug, as indicated in the description, is much smaller than even the plastic part of the original lid that holds the rubber gasket, meaning that it does not contact the edge of the frother. I tried putting the rubber ring from the original lid on the printed one, but that makes it slightly too big to fit. If the inner circle part was 1 or 2mm smaller in diameter, the original rubber ring would fit on the make and would seal perfectly.
I made my own version that fits snugly and allows for the gasket to be installed: https://www.printables.com/model/936849-xerses-nespresso-frother-lid (edited)

Since I did not get a reply from the maker of this lid I decided to create my own from scratch in Tinkercad. My version does not have a knob on it though, and is a copy of the original lid. It needs no supports, has clean surfaces all around, and is fast print. I hope it helps.
 https://www.printables.com/model/936849-xerses-nespresso-frother-lid