Make your DEX Screener watchlists public
To import your watchlists from DEX Screener, you first need to make those watchlists public/shareable.
Select the watchlist you want to import, and select "Share this watchlist" at the bottom.
Check the box to "Allow anyone with this link to view this watchlist" and then copy the link provided. If you skip this step, the import will fail.
Open the Defined Watchlists page
Navigate to the Watchlists page on the main menu, or by clicking this link.
Import Watchlist
Select "Import" from the top right of the page: 
Paste your DEX Screener public watchlist URL, give it a name and icon, and hit "Import".
You can also start an import from a token's info page under "Watchlists" In a few moments, your import will be completed and you will be able to view/share/edit your newly imported watchlist on Defined.