How to get a Rician fading channel matrix from a Rayleigh fading channel matrix?
A Rician fading  channel is just a Rayleigh fading channel with a specular (that is, unfaded) signal component.  Depending on what exactly you mean by the  Rayleigh fading channel matrix $H$, the answer could be as simple as changing the distribution of each element of $H$ from a complex zero-mean proper Gaussian random variable to a complex Gaussian random variable with mean of the form $A_{m,n} \exp(j\theta_{m,n})$.