Hi TulikaSh,
May I know whether you have follow the steps mentioned in the article to migrate Exchange 2013 Server public folders to Exchange Online? See
Use batch migration to migrate Exchange Server public folders to Exchange Online
Are users able to access Public folder via using Outlook desktop client?
If so, in the Outlook client users in your organization can add public folders to their Favorites folders. Then, depending on your organization's policies, they can use Outlook on the web to add those same public folders to their Favorites.
To add a public folder in Outlook on the web, right-click Folders, and then choose Add public folder to Favorites. Locate the folder and click Add. See
Add favorite public folders in Outlook on the web
Moreover, if you still having problem then please provide us with detailed screenshot about the steps which you have tried for further analysis
To post screenshot, please refer to steps below:
• On the top ribbon, click on Insert Image, and then Choose File to browser the picture to upload.
• Click Upload.

Best regards,
Shyamal