Under HMD Circular 4.1, you must write to the Registrar requesting leave to file further evidence and at the same time write to the other party requesting their consent to file further evidence.

You must state why you could not file the evidence earlier. The Registrar will wait for the other party's response to your request. Thereafter, the Registrar will consider your reasons and the other party's objections, if any, before making his decision.