You can use the inverse erf function, which is available in MatLab and Mathematica, for instance.
For the normal CDF, starting from
$$y=\Phi\left(x\right)=\frac{1}{2}\left[1+erf\left(\frac{x}{\sqrt{2}}\right)\right]$$
We get
$$x=\sqrt{2}erf^{-1}\left(2y-1\right)$$
For the log-normal CDF, starting from
$$y=F_{x}(x;\mu,\sigma)=\frac{1}{2}erfc\left(\frac{-lnx-\mu}{\sigma\sqrt{2}}\right)$$
We get
$$-\ln\left(x\right)=\mu+\sigma\sqrt{2}erfc^{-1}\left(2y\right)$$