First:
State, Local Agencies Remind Pennsylvanians of COVID-19 Mitigation Enforcement Roles, Advise How to Report Suspected Violations

https://www.governor.pa.gov/newsroom/state-local-agencies-remind-pennsylvanians-of-covid-19-mitigation-enforcement-roles-advise-how-to-report-suspected-violations/

And a direct link to the very difficult to find complaint form below:

I, personally, over the pat 2 weeks have observed customers in Lowes in Tarentum and Home Depot in East Liberty not wearing masks so, these stores are not enforcing mask requirements. If you observe similar in other businesses here's a link to the PA complaint form.

https://expressforms.pa.gov/apps/pa/doh/covid-19-complaint