What adjustments would you make for tuning a stringed instrument for it to emit a note of a desired frequency?

As we know,

frequency (f) = $\dfrac{1}{2l} \sqrt\dfrac{T}{πr^2d}$

Hence, frequency of a desired note can be obtained by altering the following —

(a) Length of the string — In order to increase the frequency, the length of the string should be decreased.

(b) Radius (thickness) of the string — In order to increase the frequency, the radius of the string should be decreased.

(c) Tension in the string — In order to increase the frequency, the tension in the string should be increased.