Chejar, depend if you're flying to Heathrow or Gatwick
From Heathrow, you need to take the Underground to Waterloo and you can then get a train to Southampton from there. If your test is at the Novotel, then Southampton Central station is only a few minutes walk.
From Gatwick, you can get a train to Portsmouth and then change to go to Southampton.
National Rail Enquiries is good, but you can also use
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