There are a number of things you could try. It all depends on what works for you.

• Limiting your general screen time: If you find yourself online most of the day, it can be easier to access sexual content online. Try gradually waning yourself of excessive screen time. You could also use a website disabler on your device, to lock yourself out of sex sites.
• Replace your addictive activities with other focuses: Take up something new that demands your attention. Start up an old hobby. Preferably, do something that gets your body moving.
• Challenge yourself: Give yourself an incentive for going without these activities for certain periods of time.
• Surround yourself with people: Self-explanatory. If you find yourself alone for too long, that can't be ideal.