I wasted so much time on the internet and found a solution of how do I fix the error Outlook OST file in use cannot get accessed, then I get a solution to get eSoftTools OST to PST converter software. This software has a demo version that allows users to convert OST files into multiple file formats such as OST to PST, EML, EMLX, Office 365, Yahoo Mail, Gmail, etc. It has a demo version that allows users to convert 25 items from each folder for free.