How to recover FSMO Schema master

I am trying to raise a secondary "AD DC" server on a WIN 2012. My primary server is a Win 2008. While going through the Add feature process, I got the error message:

error determining whether the target environment requires adprep unable to check

so I ran the FSMO query to verify the settings:

netdom /query FSMO

There, I noticed that the "Schema master" is a server that was decommissioned few years ago by the previous IT manager, hence, it is OFFLINE/Unavailable to respond. The current DC is just a PDC. Now, I can not go any further until I can change the FSMO ownership, and from what I have learned, the only way to transfer ownership is to perform the change from the current Schema Owner (which in my case is no longer available)

Anyone can help me out on how to recover or forcefully take ownership of my schema?