Hello, I want to reset my variables in code C++ as default blueprint like UE4 Editor do when you press the yellow arrow in editor [281240-untitled4.png] Does anyone know how can I do it?

You probably can’t do it built-in for in-game, as it’s Editor code, see FPropertyValueImpl::ResetToDefault() and FPropertyNode::GetDefaultValueAsStringForObject for example. You can always of course write your own logic to do it, depending on what do you want to achieve exactly.