If you have installed any Virto product for SharePoint On-Premise, but don't see a Virto License Manager in Central Admin, you just need to activate the Web License Manager feature. 

To do this go to Central Admin -> Manage web applications -> Select Central Admin Application and click Manage Features.

Please note: if you evaluate free 30 days trial, you don't need to activate the product - it works in fully featured mode for 30 days after your first installation!