Burried cedar collar - Can I uncover?

I have a mature cedar, about 50 years old, that looks to have had its collar buried about 2' when our house was built 40 years ago.
I want to re grade around the tree but I'm not sure if I can now just uncover the trunk.
The tree is healthy.
We had Bartlett come by and do an assessment on all our trees and they did note that the collar was buried in their report but didn't advise what to do.
The photo attached shows the back side of the tree where you can see how the landscaping was built up around it (not idea why).