First is to identify the plastic. They all use different methods for repair.
On the inside surface of the fascia there should be the molded 'recycle triangle' with the type of plastic used for the fascia in 2 or 3 letters (see the chart in the attached link). The proper repair method and finish will result is a successful and presentable repair.
http://www.bodyshopbusiness.com/Article/4129/proper_plastic_repair_procedures.aspx
On the inside surface of the fascia there should be the molded 'recycle triangle' with the type of plastic used for the fascia in 2 or 3 letters (see the chart in the attached link). The proper repair method and finish will result is a successful and presentable repair.
http://www.bodyshopbusiness.com/Article/4129/proper_plastic_repair_procedures.aspx