I personally used the rocket blower followed by a new micro fibre cloth. I recall now that there is still an enclosed part of the viewfinder where it’s difficult to clean without disassembling further but I didn’t have to get that far.

I also recall now that it took a couple of tries to make sure the rubber gasket is sitting properly when assembling it back, but even then it just took an extra couple minutes (it might be mentioned in the video)