This is called secondary referencing. You should always try to access the original source (Guastello), as Brown et al. may have put their own slant on the information from Guastello.
Many lecturers would prefer that you don't use this reference at all if you can't read the original. However, if you must use it, then you need to cite it as a secondary reference. Your in-text citation should refer to both sets of authors, and your reference list should only refer to the source you have read - in this case Brown, Sokal & Friedman.
In-text
(Guastello as cited in Brown, Sokal, & Friedman, 2014) OR Guastello (as cited in Brown, Sokal, & Friedman, 2014)
Reference List
Brown, N. J. L., Sokal, A. D., & Friedman, H. L. (2014). Positive psychology and romantic scientism. The American Psychologist, 69(6), 636-637. https://doi.org/10.1037/a003739
Please refer to the official University's Referencing Guides (linked below) for more information on referencing in the style appropriate to your discipline.
