Depends on the reason and what you find most motivating. Addiction is tricky and it’s rarely just one thing. Caffeine is physically addictive but there’s also psych and lifestyle aspects to it.

If it’s about the caffeine, try switching to coffee or tea. If you want to go cold turkey, caffeine withdrawal peaks at about three days with symptoms lessening to minimal after about nine.

If it’s a convenience thing, try keeping a water bottle on you and just drink that. If you find water too boring or your local water tastes bad, try it carbonated and/or with a twist of lemon or other fruit. I’d suggest avoiding places where they serve it, but that’s near impossible. You could take note of what situation you’re in when you tend to do it, and try to rejig your routine around that. You could also not keep it in the house; it’s a lot easier to not put it on the shopping list than resist the temptation when it’s right there. Then there’s health and money. Of course you know they’re not great for you so I’m not going to harp on that, but you could try focusing on it more (but try to frame it in a positive way; not “ugh soda is bad”, but rather “hey drinking water is good!”), or give yourself a goal to save up for purely with what you save on soda.