How to compress model texture into one ? and modify texture coordinate of vertices ?

Take input textures, put them in one sufficiently large texture using the rectangle packing algorithm of your choice. This implicitly defines texture coordinate mapping functions for each textures from their original coordinate space into the new combined atlas. Apply the respective mapping function to the texture coordinates stored with the model. Done.

Extremely general questions will lead to extremely general answers. The tasks needed to get a texture atlas are rather straight forward (although dealing with some issues like tiled textures can cause a certain amount of headache). The core of the whole issue is going to be the rectangle packing, after that everything should really fall into place. If not, ask specific questions.

Take input textures, put them in one sufficiently large texture using the rectangle packing algorithm of your choice. This implicitly defines texture coordinate mapping functions for each textures from their original coordinate space into the new combined atlas. Apply the respective mapping function to the texture coordinates stored with the model. Done.

Extremely general questions will lead to extremely general answers. The tasks needed to get a texture atlas are rather straight forward (although dealing with some issues like tiled textures can cause a certain amount of headache). The core of the whole issue is going to be the rectangle packing, after that everything should really fall into place. If not, ask specific questions.

what packing algorithm?

There are many rectangle packers with different advantages and disadvantages. This paper makes an effort to explain and evaluate several of them.

I found tools to make atlas, but don't modify texture coordinates.