Working in Germany without a degree?

Hi everyone!

My New Zealand partner and I(originally from Germany)thinking about moving back to Germany next year. (That is, I HAVE to leave NZ and we don't wanna lose each other)
Problem is, he doesn't hold a degree and we're not married either (been together for 3 years but don't wanna rush into marriage).
So, from what I've read online, he's very unlikely to get a work visa in Germany.
He spent 10 months in Germany on a WHV so his German is not bad, needs bit more improving.
He has a diploma in Fitness, worked at a gym as Fitness Instructor & Personal Trainer for 6 years.
Is there anyone who's (or has been) in a similar position and can give me advice?

ANY response will be much appreciated
Thanks,
Carina