There are plus and minus buttons next to the detailed jobs breakdowns. So you can reduce available jobs in one type to force people into available jobs of a type you need more. Usually you can then open the jobs back up and people will stay in the jobs they were assigned. In my case I needed to do some of this to get my organic pops out of the mines since I needed technicians making energy more. Robots be hungry.
This helps shift worker strata between jobs and I guess specialists between jobs (though I haven’t tried it). IIRC it doesn’t work to shift specialists down to workers though since people would rather be unemployed for a while than take a demotion.