622 is the "official" ISO actual diameter of the rim, which is commonly called a 700c for road bikes, 29" for moutain bikes.
Ask for a 29er tube as big as you can get it. e.g. 29x2 29x2.5 Because 29ers are mountain bikes, they have bigger tubes.
If you get a 700cx40 tube, it will be much smaller, and in my experience, fail prematurely.
As a matter of interest I measured a tube that was rated for 700c 30-40mm. At 30mm, it stretches of 38%, at 40mm 84%. That tube is probably OK at 30mm. When you get 700C tubes for fatter tyres, you only get the overstretched end of the range.