Cleaning a fabric gazebo

[MerkinMaker]

Does anyone have any ideas about getting mildew out of a fabric gazebo cover please?

slosh it about in a paddling pool with GP cleaner and a bit of milton or Napisan?

is it cotton, or woven polyester?

It's polyester. I hadn't thought about milton will try that.

I have put it through the washing machine but that hasn't worked.