Translation
My master does this cover against a thrust and then immediately strikes to the face or chest. And with the dagger against the sword, you always need the narrow play. Here I am close and I can hurt you badly. Like it or not, you will suffer.
Explanation
When facing a sword with a dagger, you are at a disadvantage in terms of both mass and distance. Although it is instinctive to try to stay out of reach, your only chance, as Fiore clearly says here, is to close to narrow play as quickly as possible.
As your opponent thrusts at you, move from the cover of the 1st Master to open your hips with a clockwise twist. Reach out a little and brush your dagger against the incoming sword. You do not need to push it aside, just control where it is.
Keep both your elbows in close to your body and step through with your left foot as fast as you can. The turn of your body as you do so will be enough to direct the sword blade past you. It will not miss by much, but as long as it misses, the distance does not matter. As your left foot lands, use your left hand to grab your opponents right wrist. At no stage of this move should either of your elbows be more than a hand span your hips. Extending your arms will only slow you down.
Having arrived at the position shown, you have now jammed your opponents sword. The best thing your opponent can do for themselves is let go of the sword with their left hand and use it to try and cover themselves. Their pinned arm will be closing off a lot of their movement, however, and you should be moving faster than them.
Raise your dagger, choose a target, and strike.