I’ve just installed an Invicta stove but am not sure how to fix the inclined deflector plate. Any tips?
If it’s a poêle a bois then there are lots of Invicta models.
Try entering the model on you tube and seeing what information comes up. Failing that ask at the outlet where you bought the stove, good luck 
If it’s anything like mine , its 2 plates set at approx 90°. There should be 2 interior steels, one each side set at about 45°. It simply sits on these, effectively redirecting the heat around to the front of the fire and not directly to the flue. Hope it helps.