The below FAQ page has some information about how to do this.
But I am not clear on step2 in second link. I am not sure I understand that step. Can someone explain or walk me thru on that? also what does it mean"whole procedure can be done automatically with sirilic after a brief configuration!" how do I do that?
I use the scripts that came with the SIRIL and process it and load that fit file do the stretching in Siril as explained in the tutorials.