References can be saved manually in Mendeley Reference Manager by following these 5 steps:

Steps 1-2-3-4-5: If there is one of this information as ArXivID, DOI, PMID you can easily retrieve reference data, by entering one of these data to the field (1) by clicking to the magnifying icon (2). If you don’t have ArXivID, DOI, PMID you can enter data manually. Choose the appropriate reference type. (3). Enter the related information (4) > click on Add entry (5).