Check out vMail OST to PST Converter Tool, which is the most promising tool for OST to PST conversion. It will convert OST files to PST, MBOX, MSG, EML, EMLX, and other file formats, including all attachments. After migration, users can be able to remove redundant files from Outlook. It can support all MS Outlook and Windows versions up to 10.
Know more info- https://www.vsoftware.org/ost-to-pst-converter.html
Convert OST Using Archive Method to Move Mailbox into PST
Step 1: Open your Microsoft Outlook application
Step 2: Click on “File” and then Archive
Step3: Choose the file/folder to archive and Browse the location to save the archived file
Step 4: Click Finish
Note: With the archive method, you can migrate all OST data except for the contacts.
Convert OST file to PST Using Drag and Drop Method
With this method, you can convert Mailbox items of OST file to a new PST file.
Step 1: Launch MS Outlook application
Step2: Create a new PST file in your Outlook Profile
Step 3: Choose and drag all the mailbox folders you want to move to the new PST file