Reference Cinema 4D Basic Features BodyPaint 3D Image Menu
Function available in CINEMA 4D Prime, Visualize, Broadcast, Studio & BodyPaint 3D

Flip Texture Horizontal / Vertical

Select the channels you want to mirror.

Select Transform UVW if you want to mirror the UV mesh as well.

You can select Transform UVW only if the textures in the channels to be rotated are all the same size.