three.js uv maps with fabric.js

  3d, blender, javascript, php, three.js

this is my first time using three.js or 3d modeling, so forgive me if what i am about to ask sounds stupid or too obvious

so i have a 3d model t-shirt with the uv map like this

and then i have succesfully loaded it to three.js using gltf loader, and can change its texture using canvas texture + fabric.js

but it looks like the entire uv maps is in 1 canvas like this
enter image description here

but what i tried to achieve is to separate the uv maps to another canvas, something similar with this
enter image description here

so how do i achieve it? and one more, why is the uv map flipped upside down when loaded to three.js?

Source: Ask PHP