Due to loads of Ban Appeals in Meta board recent days, I updated OP with this part:
2. Self-checking your past posts for plagiarismYou should do this before moving to the third step. Because it is your case, so you have a responsibility to self-check all of your past posts to find out that you actually plagiarised or not. If the self-check results show you actually plagiarsised, and if you did not contribute anything to the forum in the past, your story should stop in the second step.
Please copying and pasting each of your past posts into Search Box of Google Search, then enter. You finally will find your plagiarism in the past.
It might take you half of a day to finish your self-check.