Make an appearance (4,2)
(Other definitions for form that I've seen before include "Fitness" , "Group of schoolchildren < > construct" , "Establish" , "etiquette" , "Printed document with blank spaces for information to be inserted" .)
'make an appearance' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for show up that I've seen before include "cause public embarrassment" , "Expose, or arrive as expected" , "Expose or appear as arranged" , "Expose or keep appointment" , "Make an appearance" .)