The ban reason "You created or used an account to avoid an enforcement action taken against another account within this experience" means that Roblox detected you using a different account on your device or network after you have been banned.
We are using Roblox´s Ban API to prevent users from bypassing a ban. These bans are issued whenever roblox detects someone trying to bypass a ban and helps us to stop people from using accounts to bypass their moderation.
We cannot help you with finding the account that was originally banned.
You must submit the appeal on the account that was originally banned. If the account you are trying to use for the appeal has the ban reason "You created or used an account to avoid an enforcement action taken against another account within this experience" you need to use a different account.