When placing elevation markers into your views, Revit makes it easy to get an elevation of an angled wall by “hunting” for elements near the marker and snapping to an angle that is parallel to the element.
A problem comes when a design change happens and the wall the elevation was snapped to is rotated, even just a tiny bit (actually a tiny amount might be more difficult to recover from because the way Revit wants to snap.)
You can end up losing the symbolic line work in the families that are shown in the elevation and any dimensions you place will not be reporting the correct distances.
It can be difficult to get the elevation marker rotated so it is parallel to the elements you are trying to elevate again.
DON'T delete the marker and create a new one, because your ELEVATION VIEW WILL BE DELETED.
That's right, all the work put into the view will be gone for good.
Using the rotate tool from the Modify tab of the ribbon does not offer much help in this situation.
This tool allows you to free rotate the elevation marker but there is no snapping behavior like what happens when you placed the elevation marker originally.
In order to get the elevation marker to “re-snap” to the elements that got rotated in your model, you can use the rotate control grip on the elevation marker itself instead.
Select the elevation marker in a plan view and then use the small “rotate” grip to rotate the marker. When you use this grip you will notice the elevation marker will snap to elements in the model like it does when it is first being placed.
If you don't have an element to "snap" to, create a temporary wall, rotate your elevation, then delete the wall.
Or use reference planes:
Draw a reference plane from the 'tail' of your existing section to (or through) the head point. The Reference Plan should snap to both of these. This is the current 'plane' of your section.
Draw another Reference Plane that is parallel to the way you want the section to face.
Move this new Reference Plane so that it also starts from the tail of the section.
Select the Section.
Rotate. Move the rotation marker to the tail of the section.
Use the two reference planes to accurately rotate your section.