How to convert UV position to texture atlas pos and reapply to UV

I'm trying to apply a texture from an atlas to a mesh by reiterating through the UV array on that mesh, but I'm a bit lost on converting the coordinates.

For example, if the texture required is at x,y pixels on the material texture atlas, how can I convert and get those coordinates and apply to the mesh? I'm redrawing meshes dynamically with a chunk loader for a voxel game, I have it down for square voxels but now when adding more complex meshes, need to know how to apply the texture to these.

I imagine the code would be something like, but I'm hoping someone can help me fill in the blanks:

    void UpdateMesh()
    {
        UVList.Clear();
        Mesh mesh = this.GetComponent<MeshFilter>().mesh;
        for (int i = 0; i < mesh.uv.Length; i++)
        {
            UVList.Add(GetUVTextureFromAtlas(mesh.uv[i].x, mesh.uv[i].y, voxelType);
        }
       mesh.uv = UVList.ToArray();
    }
   //converts UV position expected from mesh model to position on texture atlas
   Vector2 GetUVTextureFromAtlas(float x, float y, int voxelType)
   {
         Vector2 uv;
         Vector2 textureAtlasPos = GetTextureOffset(voxelType); // returns texture pos from atlas

       //not exactly sure what this would look like for code to convert 
       //from the position on the atlas to the expected UV position based on
       //expected UV position (i.e. from 1,0 to whereever the texture is on the atlas)
         
         return uv;
   }