It will be a pain in the a with those tiny little carts. You need a small smooth paper clip with one leg unbent. And warning - you have auto batteries. Auto batteries are the ones most easy to damage or kill with leaked
juice.
Hold the cartridge, stick the paperclip in the mouth hole, push up the tiny
juice cup. Add liquid tot he juice cup until the stuffing looks just damp but not a puddle. Make sure the stuffing is stable and near the top edge of the juice cup. You can remove and pieces of foil if it was a foil covered cart. Then you need to get the juice cup back down into the mouthpiece WITHOUT pressing on the stuffing (and that means not using the atomizer to press it in). Try to use the paper clip tip against the inner wall of the mouthpiece and side against the juice cup's edge to press the juice cup back down. Then put it on the atomizer.
IMO - this kind of skinny-as-a-cig model is only good at looking nice and having nice flavor (when it works). it is inflexible and a PITA to use. I started with a similar model and I got tired of fighting with it, cleaning the atomizers, having it dump juice in my mouth. Within 3 weeks I bought two better slim models (manual Joye 510 and manual KR808D-1) that can use cartomizers.