The PPL Application form page 2 has a section for recording details of the examinations passed. This form should be complted by the RTF/FTO you are leaving showing what you have passed.
If you have sat an examination and failed but not yet taken a second attempt, the examiner will have provided you with a "notice of failure" form and will have sent a yellow copy to SRG. Provide the notice to the other RTF/FTO where you want to re-sit the paper so that they do not give you the same paper again.