https://www.reddit.com/r/AskHistorians/comments/34f637/ptsd_and_therapy_from_wwi_onwards/
These answers I've given earlier, along with the included articles, should give you some idea of treatments, at least from a British perspective.
While advances had been made in knowledge of the mind and mental health leading up to WWI, the shear amount and variety of cases that the armies of WWI had to deal with made treatment both during and after the war a daunting task to say the least. 'Shell shock' WAS acknowledged almost universally as a problem, and various treatment methods were developed, both physiological and psychological in nature, to deal with it. In the UK after WWI, many veterans suffering from 'shell shock' related afflictions were entitled to a pension, and organizations such as 'Combat Stress' sprung up to help provide for these men.
Unfortunately, the debates on just what 'shell shock' was, that continued after the war, meant that reaching a consensus was almost impossible. The commission on shell shock set up in Britain in 1922 came to a conclusion similar to that of John Vereker, Lord Gort VC, that 'shell shock' was a 'morale problem', that it was not found 'in good units'. If a soldier was afflicted by it, and it was his first case or he had shown bravery, then clemency was recommended. Recurring 'bouts' could imply a 'lack of moral fibre' or 'bad inheritance', and would probably result in disciplinary action/dishonourable discharge. This was essentially the consensus on 'Shell Shock' until some time after the second world war.
Although results were mixed, the efforts taken by professionals such as W. H. R. Rivers and Gordon Holmes during the war to treat 'shell shock' did at least serve as a starting point for later efforts.