How I can Modify weights of feedforward neural network in Matlab?

Hello

I am training a neural network with feedforwardnet using 13 neurons at input layer, 7 at hidden and 3 at output layer. The training function is 'trainrp'. I want to modify weights of this network for input-hidden and hidden-output layer with certain value obtained from optimization technique.

I basically need to check my weights when I get 99% accuracy from simple feedfordward net training and then want to modify these weights with velocity value obtained from PSO so that accuracy can be improved.

Kindly help me to know how it can be done in MATLAB.

I am using Matlab 2015.