As long as you fulfil the requirements for becoming PCO licensed (Age, Character, Medical fitness, Route finding skills, Driving ability) then the only training you will need to take is to help you pass the topographical skills assessment which is for the ‘route finding’ requirement as most of what you will be doing is driving, something which you will have probably been doing for quite a while.
You can see the exact specification for the topographical skills assessment on the topographical skills specification list page which will give you an insight into what you will need to know. Most testing centres will offer training and advice before your test although you will often have to pay for this service.
A list of accredited topographical testing centres can be downloaded here and this includes their details, costs, and also whether they provide training.
Apart from this there is no other formal training apart from when you get a job with a licensed operator who may have their own training and also your own personal training in order to keep to certain standards so that your customers get the best service.