You need police report from all countries where you been for more than 6 monthes after 18 th birthday. For Nepal, if you have any relative you can send sacnned copy of you passport first page and both side of citizenship card. Then for instance your dad or mom also have show relationship with you (eg citizenship card) or some kind of proof. Also you need to send them when you page where you get exit stamp from Neapal. Then they  can get police report from either Gausala or Ratanapark.

Hopefully this will help you