How do I put the power supply in the constant current mode?
The power supply cannot be "put" into the constant current mode. The output settings of the power supply combined with the ohmic value of the particular load determine whether or not the power supply is in constant current.
ie: The power supply inherently resides in the constant voltage mode. If the output voltage were set to 24 volts and a 6Ω load were placed across the output terminals, Ohm's Law would require that 4 amps would flow (24V/6Ω). This presumes that the constant current setting of the power supply were set to a value greater than 4 amps; let's say 5 amps. Now, if the 6Ω load were replaced by a 2Ω load, Ohm's Law would suggest that 12 amps (24V/2) would flow. However, the power supply is set to go into constant current at 5 amps. Therefore, the actual output voltage would be 10 volts (2Ω x 5A). Once the ohmic value of the load becomes greater than 4.8Ω (24V/5A), the power supply will now remain in constant current for load values between 0Ω < R < 4.8Ω.