Edit the code and change the path to where converter.exe is, I left a link so you can get it for free

Run the script, TKInter pops up

Set mipmap levels and size you want to output, default is 0 mipmaps and 512 by 512

You're limited to max 2048 px, if you're not using your DDS with GTA5, modify the code to fit your need

Drag/drop supported formats images, one by one on designated areas/rectangles

Images should be saved on same directory where the script is