using different patterns where multiple LEDs are lid to reduce the frequency.
You have to look at your charleplexing schematic and identify what leds you want on at the same time. Then work out what combination of high low and disabled states you need the pins to be in to achieve this state. Then make those pins that output state.
Problem is that some groupings are imposable to achieve like this and you have to split them up into sub groups.
Then to drive this you have to store the high, low and disabled states in an array and cycle through that array to get them to display.
This is very specific to what patterns you want to use and doesn't lend itself to a universal solution.