The following excerpt is from this article.
Training in this fashion will not only dial in and perfect technique, but you’ll be optimizing your training as well.
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To dial in something to a process is to adjust or control the process to achieve a desired outcome, like someone turning a dial on the control panel of a machine.
(also be/get dialled in) (informal)
to direct all your effort and attention on to what you are trying to achieve, so you perform as well as you can.