how I can change a parameters in fitfun in genetic algorithm in each itration of a loop?

In my code there is a loop that in each itration genetic algorithm optimizes my problem and give me the fval. How can a parameter be changed inside the objective function in a loop, meaning that in each iteration this parameter takes a different value and must be entered into the genetic algorithm? In fact, the value of the objective function(fval) after each itration should be used as an initial guess for the next iteration.

[Matt J]

If you are using ga(), constructing the loop is not your responsibility. Once you provide the fitness function, ga will run it through a loop all on its own