I tried to tidy up the network and collapsed some operators.
But how can I reverse this?
Undo is not an option, since I changed a lot of things in the meantime.
you can just select all your nodes in the COMP you created when doing the collapse (Ctrl-A) , and then copy (Ctrl-C) and paste (Ctrl-V) them them one level up. If all is connected and working again you can delete the COMP.
(if on a Mac replace Ctrl for Command button)
But the I have to make all the connections by hand?
I hoped there was a automated way. Like an un-collapse.