How to remove the back spark plug which is stuck and will not come out. on 2006 Cadillac DTS

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
The threads might be stripped. What are solutions to this problem? The other spark plugs came out just fine.
(1) Answer
you will have to excorsize little patience,and spray some WD-40 on threading. you will have to wait for it work its magic(a couple of hours). spray it on threading and take in a movie or something. now it still will not come out easy but it will come out.
remember to coat threading on replacements with never seize prior to install. good luck.