You can use the one of the greatest tool and that name is vMail OST to PST converter tool for the conversion of Offline OST files to Outlook PST and multiple file formats. It is an easy-to-use solution for opening the contents of the OST file in Microsoft Outlook. The software converts complete OST items into PST format. To ensure the correctness of the conversion, it shows preview before saving the file. The tool works well with all versions of MS Outlook and Windows OS.
How to convert an OST to a PST file
Install Recovery Toolbox for Outlook in Windows.
Start Recovery Toolbox for Outlook.
Select an OST file on the first page of the program.
Select the Converter mode mode.
View the content of the OST file.
Select a folder for saving converted data.
Select the Save as PST file mode.
Click Save.