Hi Anuja,
For making any infoobject as navigational you need to do following setting
1)Infoobject should be navigational as master data infoobject.
2)infoobject should be navigational at data target level(it can be your DSO,Cube,multiprovider).
Please do above setting at your data model then only you can use that infoobject as navigational at report level.
Hope it will helpful to you.
Regards,
Ganesh Bothe