I need help solving this problem, idk how to make it decrement if for example the value is 0.1, idk how to make it turn into 0.09. plus I don't know how to make the user choose to either increment or decrement the value.

Definitely bit the way to get the help you want here

Since when is dR the right platform to get help?

Admittedly, I'm seeing more and more such posts here that should rather be (as a well-formulated question with a minimal working example where applicable) on SO or a similar forum.