It is ten times more difficult to recapture a market once lost due to a product that has failed. This best approach to be careful in the first place and make sure everything is done right, rather than first make mistakes and than correct them.
However we all make mistakes, and it is better to learn from our mistakes and where possible correct it. In case of a filed product the very first priority should be to find out the exact nature and extent of failure. The next step will be to identify the causes of failure. Of course this means developing clarity on what all should have been done, how it should have been done, and in what ways the earlier marketing efforts failed to do that.
One obvious requirement of further action is to change the marketing approach to what it should have been in the first place. But this is not enough. As I mentioned above, recapturing a lost market is 10 times more difficult than doing the right things and capturing the market in the fist attempt. The additional nine fold effort will go into winning back the lost confidence of the customers and other stakeholders, and setting right the wrong done. The exact nature for such repair action will depend on the nature of the damage done.
For example, if the product was faulty, it is absolutely essential to redesign the product. But this is not enough, the customers will need to be reassured that the company is serious about and capable of correcting its past mistakes. It may become necessary to recall and replace or repair the products already sold. The channel partners including suppliers and distributors may need to be compensated for the losses incurred by them. Ways must be found to dispose of or appropriately deal with the material that may be still in pipe line.
All such recovery and compensatory action needs to be planned and executed with due care.