Hey kiran, Try taking feedback from the existing employees as to know any changes in the company, work to be changed.
You cannot bring back the quit employees, but you could use this as a chance to improve appraisal, more activities, motivations, etc. of the existing employees and more benefits having weekend activities, etc. It would make your work environment less tiring and better.
Once you contact your employees, then only you would understand and get to know the cause of employees leaving, so that you could work with management and do changes. Have a regular meeting with all your employees on a regular basis once a month or so to get more feedback and causes.
Hope this helps you.