Device does not reset or turn on - How to find spare parts?

We were given a broken Brondell (also branded Aktobis or Winair) air purifier. It stopped working when changing filters and Brondell doesn’t offer repairs or spare parts. [Edit: We followed all reset procedures suggested by the owner’s manual]. The device briefly turns on before turning off again. Resetting does not appear to work. There are no apparent damages to the boards (there are three, the main control board, the CO2 sensor and the user controls)

We have already tried replacing the power cord to no avail. We can’t find the problem, and can’t find spare parts that’d enable to switch and test the boards. Any recommendations?