Best answer: As directed by Ecovacs, the way to get replacement parts for your Deebot 900 robotic vacuum is to order them through Amazon.
Ecovacs makes its replacement accessory kits available on Amazon
Replacement Parts for the Deebot 900 are sold as a kit. The Ecovacs kit for the Deebot is the company that makes the Deebot series of robotic vacuums, sells the kits directly, preferring to send customers to Amazon to get replacement parts.
What's in the kit?
The Ecovacs kit for the Deebot 900/901 features replacement parts for a number of elements on the vacuums. It features one main brush replacement, which is the component you need to replace the least often.
There are four side brush replacement units. The Deebot 900 runs with two side brushes at a time, meaning that this kit offers two full set replacements of those brushes. The pack also has three high-efficiency air filter replacement units for when your vacuum's filter has been removed.
One thing that's not included in this kit is a battery. It would seem like you don't replace the battery on the Deebot 900 yourself. Battery replacement does appear to be covered under the warranty according to Ecovacs, as other parts that are the brushes or filters.