The date and other omens of “bad luck” don’t need to weigh too heavily on you ahead of your viva. Success is not due to luck. You don’t need to ward off bad luck by crossing the road to avoid a dark feline or throw salt over your left shoulder if you’re clumsy in the kitchen.
You don’t need a talisman or something lucky in the viva either. You need to have worked hard for years. You need to have learned about what to expect. You need to have prepared.
Typically, those are not too much to expect in advance of a viva.
You don’t need good luck for your viva, but you might need a good story. You might need to think again about how you got this far. You might need to remember what you did and recognise it for the confidence it can inspire.