The word "fixed" normally means: repaired, but it can also mean "not moving".
For example:
The stars are fixed in the sky.
... means: The stars do not move.
The sign is fixed to the wall.
... means: The sign is permanently attached to the wall. You can't move it.
Is your end-date fixed? Yes, my end-date is October 31.
.... means: My job is finished on October 31. The date cannot be changed.
"Fixed" is usually used in the past tense. You can use it in the present tense, for example:
Can we fix the date of the next meeting?
You don't usually say: Fix the sign to the wall.
That sounds too formal. You would say: Put the sign on the wall. Make sure it can't be moved.
