Transfer keras dataset in gluonTS

Hi. let me start by explaining some lstm Keras definition. suppose we want to predict the next 21 day stock price (21st day not first to 21st day, only 1 day) from the last 30 days history. if we have 2 features (close price and volume), our input dataset will look like [num_sample,30,2] and output [num_sample,1(21st)].
How can I implement this in the gluonTS dataset? we have a start, target and feat_dynamic_real parameters. should I set my output in target and input (num_sample,30*2) in feat_dynamic_real?
or not just set prediction_length to 21, context_length to 30 and feat_dynamic_real to (num_sample,2).