If you are citing more than one work by the same author in the same year, use the suffixes a, b, c, etc., so that your reader can differentiate between them (These suffixes will correspond to the order of entries in your References.):

Several studies (Council for the Advancement of Standards in Higher Education, 2019a, 2019b) have shown that. . .

In one study (Council for the Advancement of Standards in Higher Education, 2019b). In another study … (Council for the Advancement of Standards in Higher Education, 2019a).