Assuming that you exported your trained model as the variable trainedModel and that you have a linear model, you can access a table that has the coefficient estimates of the predictor variables as such:
trainedModel.LinearModel.Coefficients
You could extract those values by typing:
trainedModel.LinearModel.Coefficients.Estimate
You could also determine which of the predictors seemed to have the most impact by using something like LIME (Local Interpretable Model-Agnostic Explanations).
r=lime(trainedModel.predictFcn,train_data,'type','Regression');
qp=train_data(1,:);
r2=fit(r,qp,3);
plot(r2);
