As long as you have the “Use controller rotation yaw” value checked in the character blueprint and you are calling the “Add controller yaw input” function it should move accordingly.
If you haven’t done the above, go into “Projects settings”->Engine->Input and add an entry under “Axis mappings”. Name it “Turn” for example and set the binding to “Mouse X”.
When you have done that you add turning functionality like this:
Turn rate is usually 45.
Don’t forget to set the “Use controller rotation yaw” value to true.
Edit:
If you mean the mouse movement worked before but not now, it could be that the widget is taking focus. In that case try setting the input mode to game only (“Set input mode Game-Only” function) and hide the cursor (“Set show mouse cursor” to false).
Happy new year,
suzi9spal