Just popped little door back on our rechargeable Dyson, found combination of squeezing the canister and a little force (not brute) did trick for me, along with a bit of heat from a hairdryer and liquid soap to lubricate, my steps/experience below. Initially door was hanging on by the wrong side (the side with the red catches), once I realised that the usual steps to open the canister up made the door drop off as nothing holding it on any longer. Make sure you familiarise yourself with the orientation of the door, make sure you don't overlook having it the right way up, seal needs to be facing to inside of canister. Not sure if it's possible to fit upside down, you don't want to be the one to find out though. Get familiar with the little lugs on the door, as noted above mine were chamfered which must be an assembly aid, also appeared to be same length, if one is longer that's one to locate first. I warmed up the lugs with a hairdryer, no need to go mad of have hairdryer on hottest setting, just get some...

Hi, for step 8 the wider of the two ribbon cables is held by a black/dark grey clamp on the connector on the motherboard, it's best to release the clamp before pulling the cable out.

Do that by gently lifting it with a fingernail, it hinges on the screen side, it will rotate about 90 degrees to open. When reassembling it's simply the reverse, so push the cable in to the connector with the clamp open, when the cable is fully in there will be about 1mm of the gold connectors on the ribbon cable showing still, and then just clamp connector clamp shut but pushing it with your thumb.