I have so much trouble with this, I didn't even realize how twisted my thought process was until I first started going to therapy.
When you experience catastrophic thoughts, is it like a chain of events sort of thing, e.g. "if I say something silly during this meeting, my boss will be mad, spread rumors about me, get me fired, and then Ill be homeless and die in a ditch" ? Or is it the general expectation that the absolute worst thing will happen? Such as thinking "oh my goodness, I took an extra minute on this problem, I failed this test and I will fail this class, my life is in shambles"
Depending on the flavor of catastrophe you tend to experience, the approach will be different. I tend to go into a crazy chain of events, so my therapist recommended that I write out my exact thought process, or say it aloud to the mirror. Ofc talking it through in therapy is also helpful too, if thats something thats available to you. When you verbalize these thoughts, you'll start to catch how irrational they are. Look out for unrealistic expectations of others, empty spots in your "story" where you start at one point and somehow end up at another without an explanation, and all-or-nothing/black-or-white thinking.
If you tend to overexaggerate little happenings in your life, as someone said above, try to prepare yourself instead of fighting it. Think about what you'd do if that horrible scenario does happen. How can you be ready? Prepare for that! But then also think, what if that doesn't happen? What if a completely different thing happens? Sometimes while you're doing all this worrying, you'll reason through the situation and realize it's not actually such a big deal. Worst case scenario, the situation does turn end up going horribly. But you'll be prepared. You'll have a plan, things to say, actions to take. And that is so vital in preventing a further meltdown which leads to more catastrophizing.
Overall, it's about seeing your reality in a rational way. Remember that life is complex and unpredictible, yet it is also simple and constant. People don't usually care to go out of their way to sabotage you, anvils dont fall out of the sky, etc, but its normal for bad things to happen sometimes. In any case, there is always a way out of a bad situation, and in many cases you can prepare yourself prior. Catastrophizing is a normal way to prepare ourselves for scary situations. Its a matter of learning which possibilities are influenced by your disordered thinking vs. which are actually reasonable and their purpose