Why my daylight led turn red

That usually means the LED module is failing :-(. Without the year of the car I can't be sure I have the right one but these are generalized for the B8 chassis;

• Left: 8K0941003AD
• Right: 8K0941004AD

You can use those part numbers to locate the DRLs - do them both, the other one will likely fail too. You will probably have to jack the car up and remove the bottom pan to get to it unless Audi/VAG screwed it in where you can quickly remove them without lifting the car up. Without a year I can't tell you for sure how to do it, but it's going to be a screw panel or you need to jack the car a little bit to remove the bottom cover that hides the engine.