Change shock for standard RBC model

Hey, can someone here help me? I only started with dynare. In this modfile there is a positive technology shock in the RBC model. What do I need to change in order to create a shock in different variables? e.g. a shock in capital
Thank you so much

var c y i k n w r rk a z;
varexo eps_a;
parameters beta varphi alpha delta mu rho sigma_a;

beta = 0.99;
varphi= 1;
alpha = 0.36;
delta = 0.025;
mu = (delta*alpha) / ((1/beta)-1+delta);
rho = 0.9;
sigma_a = 1;

model (linear);

c = c(+1)-r(+1);
k = k(-1) * (1-delta) + deltai;
r = (1 - beta
(1-delta)) * rk;
w = y - n;
rk = y - k(-1);
y = a + alpha * k(-1)+ (1-alpha)*n;
a = z;
a = a(-1)*rho + eps_a;
y = (1-mu)c + mui;
n = (1/varphi) * w - (1/varphi) * c;

var eps_a;
stderr sigma_a;


That depends on what exactly you are trying to do. Usually, there is an economic mechanism that should be modelled.