Hi!
I wanted to drop in some advice, having been in a similar situation before. I stopped self-harming (for the most part) upon the transition to college.
The ideal solution is competent inpatient therapy where you can cold-turkey and get mental health support. I really really wish I had that opportunity, but I didn't. If you are able to do that, I would recommend it. External help is good. You can win without it, but that risk is rarely worth the suffering.
If you don't have access to proper mental health treatment, then the best strategy is harm-reduction. There are a few really good strategies that take time to master. I'm sure you've tried some already. It took me trying at the right moment for some of these to help.
1. Learn the times you tend to SH. I would always do it at night like clockwork. It helped to try and get engrossed in another activity well before that time came around. This method didn't stop anything, but it reduced frequency.
2. "Ride the wave". I'm sure you've heard this before, but addictions like this relies on dopamine rushes which lead to you performing an activity that creates endorphins. Dopamine controls many things but one of those things is motivation. It's incredibly hard to resist the "motivation" to SH, but luckily that rush is short lived. By trying to distract yourself for 5-10 minutes when the craving starts, you can often overcome the wave of dopamine and stop your action altogether. Again, this reduces frequency more than stops self-harm..
3. Get rid of all sharp things. Yeah maybe you'll engineer another method of hurting yourself, but any break from SH is a positive break. Throw them all in an outdoor garbage bin. Make them inaccessible.
4. Work to rid yourself of shame and guilt. Those are the primary drivers in non-chemical addictions. You're not attention-seeking, and maybe you should be. You need attention to your mental health. Your brain is the only thing resisting your brain right now. Of course that's difficult! We can all talk big about resisting self-destructive elements of ourselves, but that's not always possible in the moment. It always feels good to be a little fascist towards yourself, and the self-hatred following an episode of self-harm is just as destructive as the self-harm itself.
Anyway, keep engaging with recovery groups online. They are an incredibly helpful place to feel supported and valued in this hyper-isolating world. I personally care a lot about you and your recovery process!