Hi,
Are you working with a project only based on the simulator or with a hardware (so creating a project with a TBS from TouchGFX Designer or from scratch with STM32CubeMX or STM32CubeIDE)? If not just on the simulator then a touchgfx folder with the library will be generated in the Middleware/ST folder. There you can navigate and find files related to the sliders which you will be able to modify. Watch out as this files may be overwritten when regenerating code from STM32CubeMX. The other solution would be to create your own widget and base your code on the slider one.
/Romain
