Smoothing back drop

[Loo Crosland]

Hi I'm a complete beginner 

i recently just done a cake smash for a friend ( she set everything up DIY home style) now I need to edit the photos for her but being a beginner I have no idea how to smooth or get rid of all the wrinkles in the backdrop please help ? Step by step instructions would be amazing at this point 

[Damien Symonds]

Well, I'll need to see one of the photos