I created a trail O365 tenant but under the apps i don't see Yammer there. Can anyone please help me on how to get Yammer with my trail account.
What kind of trial did you provision? Most of the SKUs include Yammer, as detailed here: https://technet.microsoft.com/en-us/library/3e901a5d-ddaf-4c68-81ae-46f524311eea#bkmk_O365Service_Fa...
I have E3 plan set up but no Yammer app available. Sharing the snap shot here for available apps
Can you access the Yammer admin portal from the O365 Admin center? Or directly via https://www.yammer.com/office365/admin/success