You need to include the following:
Author (surname followed by initials) Title of review. Year month day of review. In: Title of database [Internet]. Place of publication: publisher. year. Available from: URL or DOI. Record No.: CD...
You will usually find this information on the first page/screen of the systematic review.
Example:
1. Pasquali S, Hadjinicolaou AV, Sileni VC, Rossi CR, Mocellin S. Systemic treatments for metastatic cutaneous melanoma. 2018 Feb 6. In: The Cochrane Database of Systematic Reviews [Internet]. Hoboken (NJ): John Wiley & Sons, Ltd. 2018. Available from: https://doi.org/10.1002/14651858.CD011123.pub2. Record No.: CD011123.
This example of referencing applies specifically to Cochrane Systematic Reviews. The Clinical Trials section of the Cochrane Library consists of journal references so you should reference this information using the electronic journals format.