I was in the same situation as you. I played guitar, bass, and drums and wanted to sing because I wanted to start a band and couldn’t find a singer. I joined my high school choir for free lessons and dedicated 5 day per week practice sessions. It helped a lot. I have now been singing for about 15 years, and I still have a lot of room to improve, but I can carry a basic tune pretty well. I’m nowhere near good enough to be a professional singer, but I can express the ideas in my head just fine.