Guess you simply have to assign the pins. try with the pin numbers you want to use.

take care that these pins must not be used in other settings.

I´m not familiar with Marlin ,so if it does not work try to find solution in a Marlin related Forum

Add the M7, M8, and M9 commands to turn mist or flood coolant on and off.

Note: COOLANT_MIST_PIN and/or COOLANT_FLOOD_PIN must also be defined.

#define COOLANT_CONTROL

#if ENABLED(COOLANT_CONTROL)

#define COOLANT_MIST_PIN X //where x is the pinnumber for mist

#define COOLANT_MIST // Enable if mist coolant is present

#define COOLANT_FLOOD_PIN Y //where Y is the pinnumber for Flood

#define COOLANT_FLOOD // Enable if flood coolant is present

#define COOLANT_MIST_INVERT false // Set "true" if the on/off function is reversed

#define COOLANT_FLOOD_INVERT false // Set "true" if the on/off function is reversed

Further information see here:

Marlin Support

For best results getting help with configuration and troubleshooting, please use the following resources:

Marlin Documentation - Official Marlin documentation

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