How can i convert multiple ddd into a single gtx?

[ramdompersom]

I'm editing some sprites from puyo puyo tetris. They're stored as gtx files and inside these gtx files, there's multiple images. How can i convert the edited images back to a single gtx? Every time i try only a single dds is converted as an gtx

[ramdompersom]

Also, i couldn't open some of the extracted dds files

[wzkxv]

Do you have a solution yet?