I took my 2009 SX4 in for oil change and was told there is major rust damage on the front cross member bar. What is this to how does it affect my car

The front cross member is what most of your front end suspension and steering bolt to and it's what the engine rests on. Basically it's one of the most important parts on your car and you should not drive it if it's compromised. With that said, I recommend a second opinion. It's possible it's surface rust and the oil change place isn't experienced. Either way a second opinion is needed for sure. Use this link to find a good shop near you. https://repairpal.com/repair-shops Alex