Longines is a Swiss watch dating back to the mid-1800s. Longines makes quartz watches, which are battery powered, and automatic watches, which are wound automatically when worn. You only need to remove the back of the watch to replace the battery or clean the inside, something that is fairly easy to do.
Figure out what size of screwdriver from your watch kit will fit around the edge of the watch casing. You may need different-sized screwdrivers to open the cases of different styles of Longines. Take a screwdriver and carefully place it in the crevice around the edge of the watch back. If you can fit roughly 2mm of the tip in the casing, then the screwdriver fits.
Push the screwdriver up to pop open the case. You will need to use force to open it but still be gentle in the process.
Remove the rubber O-ring or gasket. Remember to properly replace the gasket when closing the watch case. This rubber ensures that the watch is waterproof.
Although opening the watch case is an easy process, the inside of the watch can be damaged if you do not take proper precautions once the watch is open. Take the Longines to a jeweller if you do not have experience working on watches.