AnyLogic-how to randomly select agents in a particular state

I am new to AnyLogic. I need help on the following issue. I would like to randomly select agents in a specific state. I would like to set up a parameter for the # of agents selected. For example, I would like to have a random sample of 10 people in illness state. I want to make the # of selection flexible, so I would like to use a parameter to set the # of random sample size, as well. My vision is to have a slider to change the sample size in Main. I also set up a population called Patient and that will have a state charts includes health state and ill state. Among those who are in ill state, I would like to sample randomly with the number given by the parameter. Would anyone help me with this?