How do you havard reference Gibbs reflective cycle?

To reference Gibbs' Reflective Cycle in Harvard style, you would typically cite the original source where it was described. For example, if using Gibbs' work from 1988, your reference list entry would look like this:

Gibbs, G. (1988) Learning by Doing: A Guide to Teaching and Learning Methods. Cheltenham: Further Education Unit.

In-text, you would cite it as (Gibbs, 1988). If you are referencing a secondary source that discusses Gibbs' Cycle, you should cite that source instead.