The "Blue" pins are the control lines into the stepper driver, ie step direction enable and gnd.
You cannot directly plug a second stepper motor in there.
Are you using both E0 and E1? if not you can just plug the second Z into E1 and update your firmware
see Configuration_adv.h
// A single Z stepper driver is usually used to drive 2 stepper motors.
// Uncomment this option to use a separate stepper driver for each Z axis motor.
// The next unused E driver will be assigned to the second Z stepper.
//#define Z_DUAL_STEPPER_DRIVERS
You cannot directly plug a second stepper motor in there.
Are you using both E0 and E1? if not you can just plug the second Z into E1 and update your firmware
see Configuration_adv.h
// A single Z stepper driver is usually used to drive 2 stepper motors.
// Uncomment this option to use a separate stepper driver for each Z axis motor.
// The next unused E driver will be assigned to the second Z stepper.
//#define Z_DUAL_STEPPER_DRIVERS