OK great! I have attached a PDF of my Configuation.h file from the TH3D Unified Firmware I am currently using (NOTE: this is from version R2.15) TH3D has streamlined the configuration process from vanilla Marlin in my opinion.
Download the TH3D unified firmware, extract the file, and run "Openfirmwarewindows.bat". Then navigate
to the "Configuration.h" tab and make your changes. Feel free to use my settings in the file as a reference for getting the MKS genL board cooperating. Just be sure to note that I have settings for an E3D V6 hotend & thermistor, reduced print bed area for my bed clips, and the TH3D MKS gen L kit with the 12864 LCD display and TMC2208 stepper drivers. So for you I think you may only need to
- define MKS Gen L Board
- change/check Endstop Logic Settings (not sure if V3 BLTouch changes this)
- change Motor Direction Settings
- check stepper driver type settings
- define BLTouch V3
- Read through the "Extras" section, many seem to be rather useful
The BLTouch I have is an older version, so make sure you define the V3 option instead. Also, depending on what servo pins you chose, you may need to change SERVO"X"_PIN "XX", mine reads SERVO1_PIN 11.
Disclaimer any changes you make in your firmware are entirely at your own risk and I am in no way responsible, but TH3D has made this a rather easy endeavor with many safeguards.
Let me know if anything needs clarification, and best of luck Pat!