How did “dial back” come to mean “to reduce pressure on sth”

In a recent article from CNBC, they say: ”Trump will dial back his trade pressure if markets tank.”

Dial back/down is defined by Longman Dictionary as an AmE phrasal verb meaning:

to reduce something or make it less extreme.

Etymonline doesn’t mention the meaning of dial back/down, while The Grammarphobia, in an interesting piece on the evolution of the meaning of “dial”, cites:

(“Dial down” showed up in its literal sense in 1935, and figuratively in 1988, according to citations in the Oxford English Dictionary.)

It is not clear what “literal sense” referred to, anyway I’d like to know how the figurative sense of “reduce pressure on something” evolved out of dial adding back or down.

The literal sense of "dial down" and "dial back" is to reduce the level of something that is controlled with an actual dial. A good example would be volume of a sound device. In the pre-digital age a dial would be by far the most common way of controlling anything with a variable level. So your 1935 reference might be to "dial down the volume on a radio".

It's easy to see how that would evolve into reducing levels of things not literally controlled by a dial, such as asking someone to 'dial down" the level of noise they were making, even if it was not coming from a controllable device.