Also, when he said, "Turn on your flash", he is talking about a real flash, not the little LED illuminator that cell phone camera manufacturers call "flashes". There is no way the latter are powerful enough to compete with the sunlight.
If you only have access to a cell phone camera, then your best option is to put some large (ie, at least 3 or 4 feet on a side) white reflectors (clean, white bed sheets can be used in a pinch) on either side of the camera to bounce some sunlight back into the subject's faces. The difference will be night and day, and vastly better than anything anyone would be able to achieve trying to repair an image like the one you posted.
Thank you both for the advise on the flash usage. The person who took the pictures had a 'full' flash but my guess is that she didn't use it with all the pictures. But thank you for this take-away, I won't forget this...
I tried to rectify this and it works for half of the picture but the left side remains a problem area where there is still too much backlit.