If it is a branded one – for example Spektrum, then you can contact the relevant importer.
If it is 'just bought' then you have the usual purchase rights. so can go back to the retailer.
If on the other hand, it is one of the very cheap generic ones or well out of warranty, then the cost of a possible repair would be far in excess of buying a new one or an equivalent.
Year's ago, even servos could be serviced, but nowadays the examination of it plus the repair labour cost will usually be far in excess of the cost of a new one.
Hope this helps.
Paul Freshney