If accessed online then either the DOI or Available at: URL (Accessed: date) should be included (as in the example below).
Shiva, M. (2018) Socio-economic consequences of climate change. PhD thesis. University of Dundee. Available at: https://discovery.dundee.ac.uk/en/studentTheses/socio-economic-consequences-of-climate-change (Accessed: 27 April 2020).
Section G4 in CTR Harvard 12th edition.