There is no template, but formal representations just need to be based on your informal reps but updated if necessary to reflect what they have said in their rejection to your informal challenge. Nothing to panic about, anyway. If you put up a draft before submitting, we can check it and tidy it up if necessary.
The basic issue here is that if they want to wallop motorists for not putting a correct reg.number onto their parking ticket, they must first update the Traffic Regulation Order to make it a requirement. They have not done this.