Hello,
Unfortunately you cannot appeal your warning or punishments I assume in forums neither in discord which I hope we have it one day, but! unless its given unfairly against you and you think its a misused punishment then you may raise a complaint topic against the admin. Side note; read the rules of the board before creating a topic.
Complaint board:
https://gta5grand.com/forum/forums/390/
A warning isn’t as serious punishment though, I totally miss all the details of the accident but take it as a lesson and make sure you read the rules before playing to avoid such circumstances in future. Its just a friendly advise on the other hand. Hopefully you’re enjoy your stay! Good luck.