Via "User Messaging" in 'FamilySearch'.
Select the "Contact Name" of the User/Patrons; then, "Send" a 'Message'.
Here is a "Knowledge Article" in 'FamilySearch':
How do I send a message to someone who contributed to Family Tree or Memories?
That said ...
DO NOT expect a response.
We DO NOT always get a response.
There are often NO responses to 'Messages' (and, "E-mails") we send.
There are many reasons for NO response:
[ some; but, NOT limited to ... ]
▬ User/Patron has Died themselves
▬ User/Patron DOES NOT know about 'Messages'
▬ User/Patron is an infrequent User/Patron of "Family Tree" of 'FamilySearch'
▬ User/Patrons may have STOPPED using "Family Tree" of 'FamilySearch'
▬ User/Patrons may choose NOT to respond
I hope this helps.
Thanks Brett - let's hope the person DOES respond to a message !!
Of course ...
IF, their "E-mail" Address is "Public"; THEN, try BOTH ...
[ ie. "Public", being associated and viewable with their "Contact Name" ]
Nothing ventured, nothing gained ...