Advicenow has two tools to help you ask for a reconsideration of your PIP or DLA decision.
The DLA tool aims is for families with disabled children. It helps the user (an adviser, parent or support worker) to write an effective mandatory reconsideration request letter aimed at getting the decision changed at the earliest stage.
If you have to take you case further because the DWP don’t change their decision, you can appeal and use their How to win a DLA appeal for advice.
Advicenow also have a PIP mandatory reconsideration tool