You edited your answer to indicate that you are not looking to improve your singing voice, but rather to improve your speaking voice. (Your comment "it's too low" is ambiguous: do you mean only that the volume of your voice is too low, meaning that your voice is too soft and weak in character, or do you also mean that the pitch is too low and you want to speak in a higher register? You may well mean both.)
In that case, my earlier suggestion about singing in a choir might not be the most appropriate to your situation.
Since this is "Music: Practice & Theory", voice coaching for speaking is something that the participants here may have little experience with.
I have no direct experience with this, but I would also recommend that you investigate taking private lessons with a voice coach who specializes in helping people with their speaking voices. There are voice coaches for public speakers, rather than for singers. For more serious cases, there are also occupational therapists for the voice that specialize in rehabilitating speaking voices that have suffered damage due to injuries, infections, the effects of years of excessive caffeine or tobacco or alcohol, medical ailments, rehabilitation after surgery on the larynx or vocal chords, and so on. Do a Google search for occupational therapy vocal rehabilitation -vocational. The "-" (minus sign) I have included is to exclude search results that refer to "vocational rehabilitation", as that is something else altogether and search engines seem to confuse "vocal" with "vocational". If you go this route, you want to learn about vocal rehabilitation.
