Coach Mark Mapletoft has made ten changes to the side that beat hosts Argentina 48-22 with Harlequins fly-half Rory Clegg replacing Freddie Burns at ten.
And Forsyth said: "We owe Ireland one after what happened earlier in the year and there's no better place to put it right.
"They played really well that night but we know we can perform a lot better and it's up to us to produce the goods.
"It's going to be difficult but if we play the way we know we can then we should get the result that we all want."
Ireland began their campaign with a 25-22 defeat to France in pool B with Argentina next up for the French in Rosario.
Wales boss Phil Davies has also made ten changes to his side for their clash with Fiji and will be hoping for an improvement on the display in the 22-13 win against Samoa.
Dragons and Cross Keys back row Toby Faletau has suffered an ankle injury which has put an end to his tournament and he is replaced in the squad by Llandovery flanker Edward Siggery.
Davies said: "We have trained hard this week and hope to be a little more fluent against Fiji. The Samoan game was a typically hard game but the players gave 100 per-cent throughout the match which paid off with the match-winning try in the end.
"We view Fiji as a genuine step-up from Samoa, with their athleticism and off-load game very much a threat. They lost 44-11 to New Zealand but gave the New Zealanders some problems throughout and matched them physically for long periods."
In pool C Scotland coach Eamon John has handed debuts to Anthony Kent, Adam Fedorciow and Michael Fedo debuts as they bid to bounce back from the crushing 58-13 defeat to Australia against South Africa.
The Junior Springboks warmed up for the clash by dispatching Tonga 40-14 and John said: "We've committed the Australia game to our memory bank of experience.
"Playing two back-to-back southern hemisphere teams in five days is an intense environment that you have got to learn from. We've played in it, we've analysed it and now we have to learn from it."
Wales v Fiji
New Zealand v Samoa
England v Ireland
Argentina v France
Australia v Tonga
South Africa v Scotland