How to use image data with 6 channels for CNN network training in matlab

Hi, recently I have applied a 6-channel multispectral satellite image data to train CNN network using Matlan CNN code. Unlike the size of the input data 'lettersTrainSet' (28x28x1x1500), the size of my training data is 7x7x6x30,000. The difference is that instead of 1 channel my training data has 6 channels. Now while running the network training code, Matlab gives the following error: Error using trainNetwork>iAssertValidImageArray (line 575) X must be a 4-D array of images.

Error in trainNetwork>iParseInput (line 329) iAssertValidImageArray( X );

Error in trainNetwork (line 68) [layers, opts, X, Y] = iParseInput(varargin{:});

Any help on how to use training data with more than 3 channels will be highly helpful for my experiment.