The temp control knobs have little plastic tabs over the hot and cold handles. To remove them take a flat blade screw driver( small with sharp head) or a small pen knife( cover drain with a wash cloth
and pop the tabs off

Take a medium size phillips screw driver and tighten the screw

Put tab back o and you are done

If they work loos again remov e tabs, screws put loctite ( You can get a small tube for m ace or hd) screw threads and tighten

Temp control knob either has same tab or has a hex type of set screw or has a large lock nut

use a channel lock pliars over nut ( protect chrome finish by putting washcloth over then put wrench over cloth

You mentioned heads I am assuming shower head you need to use an adjuatible wrench to turn the nut (at head) and a vice rip or chanel locks over washcloth around the eustaceon ( chrome pipe coming out of wall

If you have teflon tape put that on the threads of showr head and tighten

Best of luck to you!