do you know how to find the derivative of the gamma function?
if you do - define a function like this
y = @(a) log10(a) - (gamma derivative (a) ???? / gamma(a)) - beta
notice that beta is on the other side of the equation. hence you are solving for zero now.
plot the function using:
fplot(y, [minrange, maxrange])
this will enable you to solve it graphically.
analytically, use:
fzero(y, possible zero)
this steps assume you know how to find the derivative of the gamma function.