Replacing the Bag
Lift up on the canister lid to open.
Pull up on the plastic card to remove the bag from the canister.
Note: This will seal the bag so dust and debris cannot escape.
Discard the used bag.
Install a new bag, sliding the plastic card into the guide rails.
Press down on the lid making sure that it is completely closed. Note: To achieve optimal performance with your robot and automatic dirt disposal, clean and/or replace your robot’s filter as needed.
https://manuals.plus/irobot/j7-roomba-robot-vacuum-cleaner-manual#ixzz7qWTObtfB