How to publish a value to the device memory tag from PI

Dear All,
 
I'm new to the OSI PI, i've connected to the few number of PLC's and collecting the required data's and done required Performance equations, everything is going fine and looks great, but now i'm in a position to publish a value generated in the Performance equation to the PLC Tag (Memory Register), can any one guide the procedure of publishing the value to the device.
 
My mail id is:- mrajar@gmail.com
 
Thanking you in advance
 
Muthuraja Ramu