Canon cameras use a reference image to set a custom WB. A memory card is required.

Take a picture of your workspace without any objects; it must be empty and have no outside elements to affect the WB. Full auto can be used.

Put the camera in one of the 4 manual modes (P/A/S/M). Select the red menu (Menu 2), then select Custom white balance.

Select the white reference photo. Press SET on the camera. Once this is done, the camera will save the custom white balance.