From National Rail website:
As the London Bridge - Caterham and Tattenham Corner service that normally provides 2 of the 4 Sunday services per hour to London Bridge is being diverted via Streatham this means there will only be 2 trains an hour from Forest Hill/Honor Oak Park to London Bridge at 29 and 59 minutes past each hour from 0759 to 2259.
As London Overground services that would normally operate to/from West Croydon are being diverted to Crystal Palace we will have a normal Sunday service from/to Forest Hill and Honor Oak Park.