We'll need to use Outlook self to manually convert an OST file to a PST.?

Click File in Outlook. Choose Import/Export from the list of options under Open & Export. Choose Save as a file from the drop-down menu. Choose a data file from Outlook (.pst) Choose whether to export a specific folder or the entire account. Ascertain that Include subfolders is checked. Click Next, then Finish after selecting an export destination. When the export is complete, you'll be given a PST file that you may use to import your emails into another account.