Update simulation using GUI

I have this GUI which contains a slider and a button. I want to be able to change a simulation parameter with slider while simulation is running, without stopping it or starting simulation over.

In Simulink i have a simple robot arm, which i want to rotate with slider in GUI. I tried set_param and its not working cause it doesn't change simulation in real time, it updates after I run dhe simulation again.

This is my model. I tried to change Gain value using a global variable and set_param but as I mentioned before, it doesn't work. Any help would be appreciated.