How to forecast future result using trained model

I have used the command below but the prediction does not show result beyond my trained data. The trained data is a result obtained from using the regression learner application.

yfit = trainedModel.predictFcn(starttoend)

Anything beyond the trained data gives a constant value. Is there a way to forecast future reading using the trained model?

[Asvin Kumar]

You might receive a better response from the community if you could provide more info.

Mention details about the nature of your model, the type of input. Share any code and sample data that you have.