This is how I tackled depression, I did have to leave the army for it so I understand how difficult but also easy it can be to fall into a trapped routine that makes you comfortable being depressed.
Change your daily routine is the big key here. Try sleep before 12 midnight, wake up early, go for morning walks the fresh air will hit you like a train.
Exercise is something everyone will say but it honestly can be a major difference because of how much energy you use.
Change your diet. Try some newer foods. Try avoid junk food as the way to make you feel better.
Look for a new hobby outside of work or school that doesn’t involve you hiding in your safe space (usually your home)
Try avoid sadder music that can bring up sad memories, avoid sad movies.
Most importantly SPEAK to someone. If you can’t speak to someone then put your phone on record and sit in front of it and say everything on your mind. Then watch it back. It will show you what you can’t see.