Change storage engine of MongoDB
<p>I STORAGE  [initandlisten] exception in initAndListen: 28574 Cannot start server. Detected data files in /data/db created by storage engine 'wiredTiger'. The configured storage engine is 'mmapv1'., terminating ....</p>

<p><a href="https://docs.mongodb.com/manual/tutorial/change-standalone-wiredtiger/" rel="nofollow">https://docs.mongodb.com/manual/tutorial/change-standalone-wiredtiger/</a>
I found this link thinking of any help but it says that you have to start mongod first which is not starting right now.</p>