HOW TO JOIN two surfaces in a single one

hello guys i wanna join these two surfaces but i always get 2 untrimmed surfaces aas a result i tried solid union,brep join nothing woekd help pls
even in rhino the junction is not smooth (45.2 KB)

Use Brep Joininstead…

THANKS YOU SO MUCH MATE,i got a quetion how do i make the edge surface coming off from the first surface like subd ?