Steven wrote:
Can anyone tell me what I need to do in this situation? Can I reattach
it somehow? Do I need to have someone come out to replace more than
just the cover?

Usually the cover plate assembly screws on. If you broke the bond
between the cover and the assembly that screws into the sprinkler head
then try removing the assembly by turning it counterclockwise. Don't be
a dolt and cause the sprinkler to go off.

http://www.sprinklerreplacement.com/...Residental.pdf