Do you know how I can remove the seat fabric for washing? It says it's machine washable, but I can't remove the back seat fabric and there is no instructions for this.
It can be done, as far as I know, by sliding it off somehow. It is not an easy task and I also recommend, if you truly go for it, making pictures or better yet, camera footage of how it was before and how you removed it (to be able to put it back on again).
I personally would not really machine wash it, though, stroller fabrics tend to fade or get damaged after that. I would hand wash (or if machine washed, the gentlest program there is), and with the harder-to-remove fabrics, I would actually rather keep those on and hand-washed them on the frame. Here is my stroller cleaning & maintenance article to learn more about that.