I know there are “commands” like ALIGN_CENTER, ALIGN_RIGHT etc. but is there a way to do it exactly in three quarters of the length of the screen without typing a specific number of pixels so it would be adaptive on different resolutions?
Short answer: Not that I know of.
If you have not read my tutorial, you can download it here: GUI TUTORIAL
However, I think if you are prepared to state that your module is to be played at a set resolution of 1920 x 1080, then you can build with that res in mind. Then just make it clear that playing at different resolutions will affect your GUIs.