Shortcut keys assignation

Before, when i was pressing "+" key, slider affected was Brightness

I assume you mean pressing + affected Exposure (if you are talking about Lightroom Classic, are you?).

To change the behavior of the + and – keys to work on a different slider, first you click on the slider name, and then the + and – keys will affect that slider. So, if you click on the word Exposure, then the + and – keys affect Exposure, and similarly for other sliders.