In this situation, some manageable examples may be helpful.
Take a look at some of the Collection of examples from discourse.threejs.org.
BeginnerExample
To the BufferGeometry step 2
To calculate uv’s step 12
Other examples from the collection.
RoundEdgedBoxFlat
RotateShiftTexture
UVgenerator
TextureRotationForCuboid
SphereWithoutTrigonometry
Somewhat more complicated.
TetrahedronSpecificUVs
NOTE! .addAttribute is now .setAttribute