A consequence of searching in several databases is that there are bound to be duplicates of relevant articles. The process of removing duplicates of articles is called deduplication.
You want to remove duplicates of articles, but not delete them
Why keep duplicates? Because you must document the number of articles at each stage of the review process, and this includes those duplicates. When removing duplicates, keep them in a separate folder.
To save time, check to see if your screening tool (e.g., RAYYAN, COVIDENCE) has a deduplicate function (screening tool is chosen in Stage 3: Screening)