Pick up a book with a similar style to the way you want your story to sound and start reading it. It might help refocus the voice of your own character.

Hi there, Hope you are well If I’ve already introduced myself I apologise. I can’t keep up with who I’ve said Hi to and who I haven’t. I am in your YA Group. I’m just trying to catch up with everybody slowly but surely .
Fab blog.
Eve x

When I was writing my last novel, both of my main characters voices were SO HARD TO FIND. I thought I was going to go crazy! It was like pulling teeth trying to write anything! Usually when that happens, if I keep writing, the character’s voice becomes evident, but this took longer than ANY book I have ever written. I was literally 45,000 words into the novel before the characters “clicked” and I felt like I knew them, and their voices, and what they would do and say. It was so unbelievably relieving when that happened. I could have given up before then, and then I would not have the story I have now. But it just took persistence and “keep moving forward” for me. I’d suggest that you just keep writing until it clicks, or until you find what works and what doesn’t. You might never find out what doesn’t work if you don’t keep writing. It’s like with scenes: sometimes I have to write a scene three different ways to find the ones that don’t work.

(My narrators in this particular book switched halfway, too. By that point, though, I finally had both their voices down and the second half was much easier for voice than the first half.)

Wow, I really share your pain, and I know how well things flow when you have found your stride vs when you haven’t. Can’t offer too much useful advice but I do sympathise!