Translating WS2812-LED-Strip-IDs when cutting up a strip to multiple parallel ones
No, there is no library.

It's just simple maths.

If all your strips are the same, then you just multiply the strip number by the number of LEDs per strip, and add the number of the LED you want in that strip.

So, assuming 10 LEDs per strip:

lednumber = 10 * strip + led;


You can make a little macro to do it for you if you like:

#define STRIP2LED(S, L) (((S) * 10) + (L))


Then you can use such things as:

// Set all LEDs on strip 3 to red
for (uint8_t i = 0; i&lt; 10; i++) {
    leds[STRIP2LED(3, i)] = CRGB::Red;
}