Need a hand smoothing edges and joining certain areas of the project

I’m currently working on a sun visor project for my wheelchair. I’ve made good progress, but I need some help refining the design. The main challenges I’m facing are with rounding the corners and getting a small part of the design to properly join together. For some reason, this part doesn’t want to unionise. Any help would be great !

Screenshot 2024-10-09 at 12.01.01 pm

https://support.shapr3d.com/hc/en-us/requests/new