Apart from the available sources from http://www.open-systems-pharmacology.org/ on PBPK model building workflow, how can you optimize parameters in a case were simulated data is different from observed data?
I have no experience with PK-Sim, but for "simple" parameter optimization/estimation tasks I like to use Copasi which is intuitive to use and can be used with both timecourse and steady state data (and has a nice user forum + good documentation at http://copasi.org/Support/User_Manual/). If your model is simple enough you can set it up in copasi rather quickly (or import it as SBML).
Alternatively, I recently came across a nice tutorial for using matlab's nlinfit function, which is often good enough for simple tasks: https://matlabgeeks.com/tips-tutorials/modeling-with-odes-in-matlab-part-4a/
There are multiple options for optimization. My personal requirement is to minimize or maximize target functions. There are ready to use optimized codes, which include Matlab and R functions. Depending on your approach, we can discuss. I am not a PK-Sim expert, and have never used it.