There are two main ways to either remove or hide cut marks from your arms in case it is too hot for long sleeves, or if you don´t want to wear bracelets.
The most radical and effective (but also the most painful and expensive) option is to have treatment with a laser beam or to undergo plastic surgery.
You will need several sessions until they are completely gone. It is a lengthy process, but once complete you will need little to no make up for a perfect result.
The other way is more immediate, easier and much cheaper and it involves simply covering them up with make up.
Now this cannot be any make up, as a low quality make up will not cover it up properly, it will also wear off quickly and usually in the most inappropriate settings, like when you are nervous and sweating, leaving stains all over your clothes.
Make sure to do some research when it comes to the best possible make up you could use for this, always taking into account your skin type, any allergies you might have and, of course, your skin tone.
When I looked for adequate makeup for your case, I came across the video below and I was genuinely impressed by the results!
The brand used in the video is dermatologically tested and known to be very well tolerated by pretty much all skin types.
Finally I would also suggest that instead of just covering the cuts on your arms that you also seek some professionally trained help. To really manage this, you need to find the reasons why you cut yourself in the first place. Psychologists are there to help, don't be afraid to ask for it.
I hope this helped.