Replace battery for Nixon watch
How to take the back off and replace battery
What kind of back does it have on it? Some just pop off and others will screw off. If you have one that screws you will need a special tool to remove the back. This looks like a more expensive watch however some watches will have what appears to be a back that screws off but they are actually pop off. This is usually on cheaper watches to give them the appearance that they are more expensive watches.