If the file is ready, from within the efile,  just hit the Efile now button and pop ups will guide you through the process. If your in the homebase, select the file, then Efile>Electronic Filing>Convert/Transmit Returns/Extensions/Payments... then pop ups will guide you throught the rest. 

You can use the EF Now button in the EF Center of Homebase too!

Here's the official article on How to Efile in Proseries

How to e-file a tax return in ProSeries