You should search multiple databases when doing a systematic review. This will often lead to duplicate results, though each database will probably have some unique publications as well.
Most databases allow you to export search results into citation management software. The following are some of the most commonly used citation management software. The link will take you to the library's information page for that software.
While these tools have an option for removing duplicates, that feature is not always accurate. You may need to manually look through the results list as well, perhaps sorting by author and article title and then skimming the list of references.
Once you have removed duplicates using citation management software, you can upload the records into systematic review software that will allow you to screen each publication for inclusion or exclusion and also to code the publications. Rayyan is once such tool.
While Rayyan has a de-duplication option, it is best to bring in a de-duped set of references from citation management software.