Sometimes what helps me is to look at the bathroom mirror and talk to myself like a crazy person lol. Just look yourself in the eye and and go "I'm so miserable and my life sucks." You can mouth it out too. After a couple minutes I'll look away and start crying.
You can also try listening to your favorite sad songs. I love to listen to musicals, since certain songs can take you right back to a sad scene in a show. If you have time, you can try depressing movies too. Or those "try not to cry" challenge compilation videos on YouTube. That Thai commericial with the girl who adopts a baby she found on the street always gets me. Journalling can also help.