Try this or google consolidate tracks from mono to stereo
Select the whole mono region and consolidate it. (Alt-shift-3)
Rename the new region XXXX.L.
Select this region and consolidate it again.
Name the second consolidate XXXX.R.
If you used the exact same name between the .L and .R files, they will create a stereo pair in the regions bin. Find this region in the bin and drag it to a stereo track.
Best Of Luck
Christopher