You see, whenever possible, we have to try to hold ALL the fingers on the keys at all times. Regardless whether that finger plays or not, the most efficient way of playing organ manuals is by keeping your fingers on the keys.
Sometimes we forget to do that, especially when the hand changes position. In this case, you have to slide the hand horizontally across the manual and don't lift it up into the air.
Often we try to keep the fingers in contact with the keys but we forget about the 4th and the 5th fingers. They usually are held up. Especially the 5th finger. Whenever you catch yourself doing this, relax ALL the fingers and let them rest on the keyboard waiting in the correct position for their turn to play.
Keep this in mind and you can control the touch much better, depress the keys at the precise time when needed, release the chords exactly together, and even avoid many mistakes while playing the organ.
Modulation from Bb Major to F Major: I-V65-I=IV-II65+-I64-V-V7/6-I-I64-I