Have you tried the Create Best Fit Profile command?
You can access it from the ribbon by selecting a profile view and it should be on the Launch Pad Panel of the Profile View context tab of the ribbon, or type the command CreateBestFitProfile.
You can select the surface that you want to use as the source, or other objects.
You will probably have to play with the parameters in the dialogue to get a result you want.
If a post provides a fix for your issue, click on "Accept as Solution" to help other users find solutions to problems they might have that are similar to yours.
Andrew Puller
Maitland, NSW, Australia
Windows 11
Intel core i7 11800 @ 2.30 GHz with 32GB Ram
Civil 3d 2023