There isn't a direct way to upload/import a watch list; Here's something that you can try.
1. In Excel have all your Watchlist in one column.
2. Select the entire column and copy it.
3. Open your portfolio or create a new one, go to '+ Add Symbol', paste the selection, and hit 'Done'
Your desired watchlist tickers will be added to your desired portfolio.
Customer support service by UserEcho