Fare rules are different than in the US, so assuming you don’t have a flexible ticket, any voluntary change will come at a high price. So high it can exceed your total ticket price. Or beyond since it’s a mileage run and probably a deeply discounted ticket.
And as Irish Guy mentioned above is that European routes tend to be totally packed, especially on a high volume route like AMS-CDG vv.
The only realistic option you have is that there might be irrops so you have an excuse changing your ticket and that will have to be done by AFKL ticketing to be contacted via SoMe. That’s your best bet imho. The lounge in YYZ don’t have the rights. They can swop seats. That’s about it.