When co-workers are careless with their jobs – become a leader
As frustrating as it may be, use these times as an opportunity to become a leader and show your leadership skills.
When approaching your boss and informing them of the situation, let them know that you would like to help lead the colleague with getting their workload done.
Then approach your colleague and say you want to help them meet goals and deadlines. It will prove that you can deal with difficult situations and be a leader.