How do I stop being so nervous before tournaments?

First: you don't need to stop being nervous, you need the nerves to stop costing you touches. Every fencer on that strip, including the one seeded first, has adrenaline. The ones who look calm have routines, not different biochemistry.

What actually works, from sports psychology and a thousand fencers' experience: (1) Warm up properly, nerves live in an idle body; footwork and stretching literally burn the jitters. (2) Have a between-touches ritual, fix your glove, tap your mask, one breath, en garde. The ritual gives your brain a familiar place to stand. (3) Set a process goal, not an outcome goal, 'I will finish my attacks today' survives contact with a better opponent; 'I want to win' shatters on the first lost bout and takes your composure with it.

Reframe what a tournament is: at your first events you are literally paying for lessons. Every pool bout is five touches of information about what works under pressure. Losing 5-2 to a stronger fencer while doing the thing you practiced is a good day.

And the unsexy one: eat, sleep and hydrate like it's a sport, because it is. Half of 'tournament nerves' at 2 PM is a fencer who's had nothing but adrenaline and a granola bar since 7 AM.