Do you mean the fabric has stretched? If so, you can turn the roller tube another turn or two to add tension. The method of doing that depends on whether it is an A&E slide topper or a Carefree topper. Manuals are available on the awning manufacturer web sites.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL