I’m assuming you mean Exeter and Exmouth England, not London. You always used to be able to take the train from Paddington Station in London to Exeter and then a local train to Exmouth, but since Britrail was broken up in the 1980s, much has changed for the worse in British train travel. I would Google it and see if you can find out what trainline is servicing the Southwest (county Devon) where Exeter and Exmouth are located. It is likely to be a journey of several hours.