You can easily remove the mattress cover by opening the zip on one of the short sides. Machine wash the mattress cover separately in hot water. Use a gentle, bleach-free detergent. Do not tumble dry.
It is also easy to remove the fabric from the travel cot by opening the four zips around the frame. Machine wash the fabric separately in warm water. Use a gentle, bleach-free detergent. Do not tumble dry any of the parts.
The mattress itself is too large to be machine-washed. You can wash it gently by hand and rinse it off as needed.