Actually, six months is still pretty short, so your cardio is gonna improve naturally just by keeping training - but you can definitely speed it up. The guys already said valid stuff about interval training and specific work, now I'm gonna add something most people ignore: varying your breathing type during training makes an absurd difference. Like, when you're doing shadowboxing or heavy bag work, try breathing deliberately in different ways - exhale on the attack, hold your breath on defense, breathe through your nose only during rest moments. Sounds dumb but your body learns to optimize oxygen at the right times, and that saves you when sparring gets intense.
On top of that, building on what they said about interval training, the ideal thing is to do work rounds that simulate exactly what happens on the mat - but with intensity variations within the same round. Like, the first 20 seconds you go 100%, then 40 seconds lighter recovering, then 20 seconds explosive again. Do this with exercises that combine cardio and strength in the same movement: burpees, mountain climbers, jumping rope at different speeds, it all works. Half a dozen rounds like that, 3 times a week off the mat, is gonna change your conditioning in 4-5 weeks.
Another practical thing: always do anaerobic exercise after aerobic work during the week, not before. Your body's more ready to absorb strength training when it's already burned energy, and you avoid injury. And drink water during specific training sessions, don't wait til after - hydration keeps your cardio more stable.