change a arduino code for midi controler usb 32u4

this is arduino midi controler project with faders pots and switches. I will have 42 controls available one 16 channel multiplexer will be digital (switches) and two other ones will be analog (faders and pots). i need someone to make this code handle 3 multiplexers instead of one using this model https://fr.aliexpress.com/item/32858973834.html?gatewayAdapt=glo2fra&spm=a2g0o.9042311.0.0.154c6c37NGCiR8 and i need the midi information to go through the usb plug and keep the existing midi plug possibility for later. I have found a code that needs to be changed so that 3 multiplexers are used (1 digital 2 analog)

code included is from project
https://www.notesandvolts.com/2016/07/arduino-midi-controller-multiplexers.html


this is my first midi controler so i have a small budget !