That’s Marvelous Designer I am afraid. 
I have tips for that though. The main thing would be to cut the curtain in any way that you like and freeze parts of it when simulating and only re-simulate what needs changing and keep parts that you like. I am not sure how to do this in Blender like that… I kind of needed all the properties of the fabric MD offers to see what sort of fabric folds the way I like most and also to simulate it in reasonable amount of time changing the density of the fabric during the process(start with rough simulation, then add detail only when everything is roughly in place already)…
It would be a really really hard task to do this in Blender… at least for me. 
I hope the new geometry nodes cloth simulation coming to Blender just now is going to make things like this easier, but… even then it seems to have a lot of missing features for that or some of them are not even planned as far as I can tell.