Revert anayltic signal(length(N/2)) to real signal (length(N))
First answer deleted since I completely misunderstood the question.

The problem here is that apparently you are missing one frequency point. From the question it's not clear what is missing. You say you have the points from 0 to N/2. That's actually N/2+1 (if 0 and N/2 are included) and all you need. If that's not the case, there are gew possibilities


Go to the person who provided the data and ask them to fix it
X(0) and X(N/2) are actually real valued. Sometimes people pack the X(N/2) value into the imaginary part of X(0) to save space and create a symmetrical representation. Check your X(0) and figure out whether it's imaginary part is actually 0 or not
There is a way to represent a N-point real sequence with exactly N/2 complex coefficients that involves a  half sample rotation in the frequency domain. That's pretty esoteric and unlikely in this case (but works quite well).
If the high frequency energy in your original signal is sufficiently low, you can set the Nyquist coefficients simply to zero. According to the sampling theorem, that should be zero anyway. In practice this will add some noise to the reconstructed signal but if it's small enough that may be tolerable.