http://eng-ca.faq.panasonic.com/app/answers/detail/a_id/42530/~/how-do-i-adjust-the-white-balance%3F---dc-fz80 seems to tell us to press the AWB button and it appears to be doable in manual mode.
If this fails, check for new firmware at the maker's site before you call it in or go for a refund as defective.
When I am on Manual mode on my Lumix FZ80/82, it won't let me change the white balance. It's automatically in AWB. But, when I move to C mode (which I don't know what it is), it lets me edit the white balance, but I can't edit the Shutter Speed, ISO, or the aperture. I would like to be in manual mode (so I can change everything), but I also want to change the White balance... Could anyone help?