I’m doing this from memory without the app to look at, so excuse any inaccuracies...
First click the “auto” button (bottom left) to switch to “Pro” mode.
Then individually set ISO, Shutter, or WB to your desired setting. Each has “Auto” as an option on the left. So you could lock in shutter, lock in WB, but let ISO get set automatically.
It’s probably not a good idea though because higher ISO’s generate increasing amounts of noise. Neat Video can do wonders with removing noise, but it’s time consuming (especially if you’ve never used it before) and it’s very very processor intensive. Anyway, good luck.