I have applied for a Schengen-Visa few days back. Today I got a mail from the airline reservation desk saying that my flights ( both up and down)are cancelled due to some operational issues and gave me an offer to fly on the closest available flights (one day prior to my original dates). Will it lead to a visa denial? What do I do in this situation?
No it will not. The flight reservations are part of documentation you provide to establish the nature of your itinerary. You are free to change the flights dates and times.
The only impact it has is on the validity period of your visa - especially if this is the first time you are applying.
The embassy may choose to pin you validity dates to within +/- a few days of your supplied itinerary.