Chicken is okay to eat after use by date as long as it has been frozen and not spoiled.
The use by date on chicken is just a general guideline as to how long the chicken will remain fresh and does not mean the chicken has actually gone bad.
Frozen chicken can still be safe to eat even 6 years past the use by date as long as it's been frozen.
There have been times where I have forgotten about some meats including chicken at the bottom of my deep freezer and then 5 or 6 years have passed and I'm cleaning out the freezer and I discover I still have some chicken and other meats at the bottom of the freezer.
I have safely eaten that chicken and meat without any issues.
The chicken and meat is not as fresh after all those years but it's still safe to eat.
However if the chicken was just in the refrigerator then it can go bad after 3 to 5 days so make sure to either freeze it or cook and eat it before it spoils.
There's no need to throw out chicken or meat just because it's past the use by date as long as it smells good and has no really slimy texture to the skin.