You cannot change part of your photo TO a particular chosen colour, you can only apply a tint OF a particular chosen colour over the the top of your photo.
The resulting colour always depends on the starting colour. If you want to achieve a particular finished colour then you will need to set the overlaid adjustments accordingly - by eye. That will often not be possible with just the colour tint adjustment: this is like applying a colour dye. All you can set there, is what hue and how strong. So if you have a pinkish starting colour of an object (say), and you want to achieve a more grey colour of a different hue character, this tool can paint on a bluish or greenish "dye" opposed to the unwanted pink - this will be quite tricky and demanding to do and still may not manage the desired effect on its own.
A more powerful approach might be two-pronged:
include some negative saturation adjustment in your local adjustment, enough to tone down to the needed degree the strength of that unwanted pinkishness (say), at source, from areas of the photo. Also some tomal adjustment if you want to simulate a darker or lighter coloured surface, or one that reflects light in a shinier or duller way.
Then, you can include (either in the same brushed adjustment or in another one) some corrective white-balance temperature or tint adjustments, and/or use the colour "dye" tool, for changing the hue character of that range of colours you've painted over, in a fairly natural-looking way.
It is very often the case in Lightroom, that it's the right combination of adjustments which does the trick.
You can monitor the resulting colour values after your adjustments, and compare them against a reference, by watching the numbers below the histogram as you move the mouse pointer across the photo. Those numbers are LR-internal % values unless you use a soft-proofed view for e.g. sRGB, which will then preview that output. However a typical real-world photo of a surface of a certain colour, shows all kinds of variations due to direct and reflected lighting, affected by nearby or ambient surfaces etc in complex ways - so it's your visual judgement of whether something LOOKS believably like a portrayal of the desired colour, that is more important than those numbers.
We can only use those numbers absolutely in very controlled circumstances, e.g product photography in a studio setup.
But if within the same photo there is a reference we can compare to, then we can use these numbers relatively. Say, if someone in the photo has (what we know to be) a "white" or else "grey" hat on, if we can local-adjust a wall to show roughly the same R/G/B proportions as the hat shows, that wall should accordingly appear as if it had a "white" or else "neutral grey" appearance in real life, same as the hat does.