There is a small gap in the back cover of your watch, use the watch opener to pry it open with a little force, prepare the battery that matches your watch model, remove the old battery with small tweezers, install the new battery, then put the fixed frame in the watch, put the waterproof ring on the back cover, apply a circle of watch waterproof oil, and then align the position of the back cover, but this needs: Two thumbs press hard at the same time, this time the mirror side needs to use a soft cloth cushion, if not a new point of the dry towel is also OK, must be soft, to ensure that it will not grind the mirror.
Or put the towel or soft cloth on the wooden table, put the table on the table, and then align the back cover with the installation, and then put the soft cloth on the back cover and tap the table hammer to install it
The back cover without screws is a press fit type