The set iteration command permits the user to change the iteration number for the Marquardt-Levenberg nonlinear fitting method. See set function. The default value is 10. However, the fitting process will stop if there is no difference in χ2 for two consecutive iterations. However, a negative value will force to iterate up to the absolute value of that number, without checking for convergence.
set iteration value
set iteration 3
fit, set method, set function