Converting OST (Offline Outlook Data File) to PST (Personal Storage Table) manually involves exporting the data from the OST file and importing it into a new PST file in Outlook. Here's a step-by-step guide on how to do it:

Create a New Outlook Data File (PST):
a. Open Microsoft Outlook on your computer.
b. Go to the "File" tab and select "New" > "Outlook Data File."
c. Choose the PST file format and click "OK."
d. Provide a name and location for the new PST file, then click "OK."

Export Data from OST to PST:
a. Make sure that the OST file and the newly created PST file are both accessible in Outlook.
b. Go to the "File" tab and select "Open & Export" > "Import/Export."
c. In the Import and Export Wizard, choose "Export to a file" and click "Next."
d. Select "Outlook Data File (.pst)" and click "Next."
e. Choose the folders or items you want to export from the OST file. You can select the top-level mailbox folder to export everything, or choose specific folders.
f. Select the newly created PST file as the destination for the exported data.
g. If needed, choose the options for handling duplicates or replacing items during the export process.
h. Click "Finish" to start the export process. Outlook will transfer the selected data from the OST file to the PST file.

Import the PST File into Outlook:
a. In Outlook, go to the "File" tab and select "Open & Export" > "Import/Export."
b. In the Import and Export Wizard, choose "Import from another program or file" and click "Next."
c. Select "Outlook Data File (.pst)" and click "Next."
d. Browse to the location of the newly created PST file and select it.
e. Choose the options for handling duplicates or replacing items during the import process.
f. Select the folder where you want to import the data or choose to import it into the same folder structure as the original OST file.
g. Click "Finish" to start the import process. Outlook will import the data from the PST file into your mailbox.

Greetings,
Peter