You can import the OST File into Outlook manually but there you can find many flaws and are quite irksome and even may lead to the loss of important databases. Sometimes, the latest edition like the Outlook 2016 version is also not encouraged. So, the better option is to use SysInspire OST to PST converter with the help of which there will be no complication to import the OST file in outlook. Only 3 steps far from conversion 1. Browse Your OST File 2. Scanning process 3. Conversion.
Read more info:- import the OST File into Outlook manually