You have to file a defence or Acknowledgement of Service by 11 May, if the latter this gives you until 26 May to file your defence.
Your defence is as above, that the defendant is a hirer of a car, the driver of the car was not identified and the claimant did not follow the requirements of PoFA 2012 to transfer liability to you as hirer. You need to elaborate slightly and briefly quote the legislation and that the required documents were not sent with the Notice to Hirer.
It being DCB Legal means that they will likely harrass you offering to “settle”, then discontinue, if you follow the court paperwork, submit N180 when required and attend a useless mediation session. Search the forum for many, many similar cases and their outcomes.