Using SPECIAL-K.
Setup SPECIAL- K first: Getting started | Special K - The Official Wiki (special-k.info)
Extract archive to your Special-K installation
C:\Users\%username%\AppData\Local\Programs\Special K
Add your game to Special-K if you haven't already done so (automated process)

If you click on "Centralized", it will open Special-K path directly to the profile folder you're using to load textures in GBFR.
Launch your Game through Special K!
or
add this parameters to your steam game launch option (Granblue Fantasy: Relink)
then launch your game through Steam directly and Special K will start.
SKIF %COMMAND%
You have succefully loaded DualShock 4 Button Prompts!