To import the PST calendar to Office 365 manually, one should follow these steps:

1. Launch Microsoft Outlook on the system.

2. Click on "File" and then select "Open & Export."

3. Choose "Import/Export" from the options.

4. Select "Export to a file" and click "Next."

5. Choose "Outlook Data File (.pst)" as the file type and click "Next."

6. Select the calendar folder for export and designate a location to save the PST file. Click "Finish" to complete the export process.

Challenges encountered during manual import include:

- Time consumption, particularly with large PST files.

- Risk of data loss or corruption if the import process is interrupted or executed incorrectly.

- Potential compatibility issues between Outlook versions or Office 365 configurations.

Alternatively, users can simplify the process by utilizing the Cigati PST Converter Tool. This tool provides a straightforward solution for importing the PST calendar to Office 365 without manual intervention. With its user-friendly interface and advanced features, the Cigati PST Converter ensures a seamless and efficient conversion process while maintaining data integrity. By utilizing this tool, users can overcome the challenges associated with manual import and effortlessly transfer their PST calendar to Office 365.