Hi there!
We have offices in Detroit area, Chicago area, Seattle area and Minneapolis area. Considering there are many differences in each area and what their cities are facing (COVID and protests), we more so leaned into what made our employees feel comfortable. We've seen rather positive results while employees are working remote - increased efficiencies and reduced errors - so for us, it wasn't a 'forcing back to work' situation. 
We released an optional survey to allow those who wanted/needed to return to office to respond and confirm what days they'd need to be in. 
After that, we set up a required training and launched an app that they have to attest to any symptoms/exposure prior to entering the office each day. 
So far, only 2 offices are open and with very small numbers of employees going into the office, but it is going well *knock on wood*

Here is an HR Toolkit and Book of Checklists to help the transition back to work for everyone! Hope it helps!