Did this once by accident years ago to my old international p/u. Half a tank of diesel before noticing, coming from a night of drinking and dancing, had a hot chick in the truck, Hey, I was distracted. After my boo,boo I just topped it off with premium, called it ethyl back then and went on my way, never a hiccup. No fuel injection to worry about tho, that might be a problem here.
I'd just suck/siphon out as much as possible and fill it with premium gas and go for it. Maybe run some injector cleaner thru it at the same time.