There is no trick with scrolling.

You display one image.
You repeat the same image the number of times needed to get a specific scroll speed.

Then you display one image that is shifted sideways one pixel.
Repeat this display for required number of frames.

And as already noted.

You either build the bitmap on-the-fly, keeping track of how many pixels into the character your current scroll is - but you must have a buffer that stores all characters in the scrolling string.

Your you build a single bitmap that contains all the text. Then you just step the start position when emitting the bitmap.

You either use a language that you know. Or you learn a language (or assembler) good enough for you to manage to implement this feature.

You can emulate the display by emitting 8x8 characters on a PC - one character for each LED. Print the bitmap. Wait a number of ms. Emit next bitmap. Experiment until you understand how it works. Then back to your real hardware.

By the way - This thread is getting long, but I still don't think you have given a full description of how your hardware interfaces the diodes. Without that, people can not tell what to do to emit a single bitmap.