When you twist someone's nose, this is an example of tweak.
When you make small adjustments to a car's engine to make it run optimally, this is an example of tweak.
A small adjustment made to the engine of a car to make it run better is an example of a tweak.
Tweaked her sister's ear.
Tweaked her computer setup.
Made a few tweaks to the sound system.
He is running so many tweaks it is hard to remember how it looked originally.