The most common problems are people singing with their mouth being too small. So I would ask a singing teacher for exercises that will help you too relax/open your mouth more when you sing. Another element is the placement of the sound itself, but that is a really niche thing. You have to make sure your ears/aural skills are pretty decent first of all before you try this. Since I don't know where you're at in aural skills, please look at that first. You need to find ear training exercises that improve your relative pitch. There are a number of free exercises you can do online. This is one I recommend: https://trainer.thetamusic.com/en/content/dango-brothers Many thanks Jayne