In order to cite MRI-Simmons, you will have to indicate the study you looked at (NHCS Adults, Connect and associated year) as well as a description of the data retrieved. Here are some examples:

Crosstab results citation example (NHCS Adult Study):

MRI-Simmons (2019).  Spring 2019 NHCS Adult Study 12 Month [Ice cream/brand most used by consumer demographics - gender].  Retrieved from Simmons Insights, https://insights.mrisimmons.com/essentials/quickreports.

Quick Report - Demographic Profile (Simmons Connect Study):

MRI-Simmons (2019). Spring 2019 Simmons Connect Plus [Target/Baby boomers and reading books] [Demographic Profile]. Retrieved from Simmons Insights, https://insights.mrisimmons.com/essentials/quickreports.