you will have to contact customer support to get you Merchant code and category changed.

https://squareup.com/help/contact

Click "Other"

Click "I don't see my issue"

Click "Call Support"

Write down your Customer Code

Call 1 (855) 700-6000

Depending on your specific account, you might not have phone support available, or you might have limited hours of support. If your account doesn't have phone support, Email is the only way to communicate so that there is proper documentation of the conversations.