Hi @Ramaswami - we use ReturnPath seeds as well and I have set up an Import job to process the list when they release a new Seed List.
Read this: https://docs.adobe.com/content/help/en/campaign-classic/using/getting-started/importing-and-exportin...
Save the Excel file as a CSV file (the one you have opened in Excel is probably already a CSV). Then create yourself a new Simple Import job with the following Field Mappings (Seed Folder Internal Name is the internal name of your seed folder and Seed Label is ReturnPath<%= source.recordIndex %>)
Once you have the Import Job ready to go, then delete all the existing seeds in the Seed folder and run the import job.
Cheers