Opening locked field before recreate new label name

ear All,
I am currently adding additional label behind the field label/name.
what I need for example in field Phantom, I want to add sign , so
the field label to be Phantom (
I open the form layout from setup (right click setup), then go to
tab reference, click + to drill down the BOM, but i surprised
because the field phantom contains lock sign, I can’t then
write the new label in the properties section.
Could you let me know how to open the lock ? is it fixed or not ?
tks in advance for your answer.