Wet the area down that needs to be shaped. Wicker is quite resilient and will keep the form that it dries in. Allow it to air dry.
Apply linseed oil to dry cracking areas with a clean cloth. Allow the furniture to soak in the oil for about 24 hours and reapply until it will not absorb any more.
Sand loose spots that are causing roughness with a small piece of fine grit sandpaper and spray lacquer on it to help keep it smooth. Allow the furniture 15 to 20 minutes to dry.
Weave a new strand of rattan into the furniture if one needs to be replaced by gluing it to the bottom or back of the furniture. Choose the least noticeable spot. Weave the new strand in where the old one was and glue it at the top in the back again.