Using NARX neural network to predict using only inputs

Hello,

I'm new to neural networking, but I created a NARX network with the ntstool and now I want to use it to predict data without including the output. Is this even possible? I used soil mositure, soil temperature, and precipiation data and fit it with soil respiration. Now I want to just use the input data to predict soil respiration for another year. I tried using the predict function, but just returns "no valid system or dataset was specified". I also tried just using the matlab generated function, but it needs to have an ouput in order to use it.

Thanks in advance for your help.