How do I fix the colors in this video?

A recent recording turned out to contrasty and to saturated. Maybe there also is a slight yellow tint.

I never color graded in Davinci Resolve. What's the easiest fix?

That's like saying "My car won't start, and I'm not a mechanic. What's the easiest solution?"

Well, the 'easiest' is to take the car to someone who is a mechanic. Or in this case, give the footage to a professional Colorist.

If you're set on doing it yourself...
https://www.blackmagicdesign.com/produc ... e/training

Here's a couple of quick things you can try. If they don't improve things they can be undone with Ctrl+Z.

Using the White Balance tool I should have said "Move it to something in the scene that should be white and click on it".

I'm sorry for the lame question. I tried measuring white balance on the white microphone but it doesn't help.
Can you point me to a good introductory tutorial with the basic of color grading in Resolve? What I saw misses the point or is aimed to larger productions.

Apart from The Blackmagic training videos there are plenty of tutorials on YouTube. These may be of interest.

https://www.youtube.com/c/LearnColorGrading/videos

Thanks!

Can you point me to a good introductory tutorial with the basic of color grading in Resolve? What I saw misses the point or is aimed to larger productions.

I found Daria's introduction to the Color Page in DaVinci Resolve to be excellent. You can find it on the DaVinci Resolve Training page under "The Art of Color Grading". She covers the basic stuff like how to use the color wheels and curves first, and that may be all you need - but I think it's worth watching all the way through to get an idea of what's possible. It's well worth downloading the sample files and following along in order to really let the material sink in.