You probably can't do it online - most train companies only support "simple" cases on their websites including only their trains and stations

Frankly your easiest option is to take a photo of the ticket, then email it to cross country trains (not virgin) along with details of what trains you caught and what you intended to get, and the final delay length. They will reply back a day later saying "sorry you were late, but as the first delay was virgin we've sent your complaint onto them". A week later Virgin should post you vouchers / cheque as requested