Try doing the combos calmly and cleanly in training so that you’re relaxed instead of tense when doing them. You need far less force to get the stick to move fast than you might think, and there’s far more time to do things than you might think.
Then do the combos again. And again. And again ad nauseum.
Also practice hitconfirming into them - set the dummy on random block, do a couple lights and only continue into the combo proper if the lights hit. (the purpose of the light moves is to give your brain time to recognize whether the opponent is blocking or not - human reaction times are far from instant).
If you practice those things a lot, the rest is just about getting used to doing them under pressure, which again comes with repetition. Just set it as a goal to hit the confirm into at least part of the combo at least once a round, winning or losing be damned. There’s no magical shortcut to it, just work. Just remember that it’s entirely humanly possible to do, and the difficulty is more about you being unfamiliar with doing it than it being superhumanly hard to do. So get familiar and start wrecking other newbies >:)