Modeling inter-occasion variabile

Hello,
I am working on modeling meta-analysis data that have studies that is considered as individuals and response collected one a few time points. Also each study has two arms which will be defined as an occasion and estimate IOV.
My question is how to add IOV to the model. I am using the Metrum institute as template as shown below:

//doseResponseMBMA1
data{
int<lower = 1> nStudies;
int<lower = 1> nArms;
int<lower = 1> study[nArms];
real<lower = 0> dose[nArms];
vector<lower = 1>[nArms] n;
vector<lower = 0>[nArms] response;
}

transformed data{
vector[nArms] logResponse;

logResponse = log(response);
}

parameters{
real<lower = 0> e0Hat;
real<lower = 0> emaxHat;
real<lower = 0> ed50;
real<lower = 0> sigma;
real<lower = 0> omegaE0;
real<lower = 0> omegaEmax;

vector<lower = 0>[nStudies] e0;// arrays works too
vector<lower = 0>[nStudies] emax; // arrays works too
}
transformed parameters{
vector<lower = 0>[nArms] responseHat;

for(i in 1:nArms){
responseHat[i] = e0[study[i]] + emax[study[i]] * dose[i] / (ed50 + dose[i]);
}

}

model{
e0Hat ~ normal(0, 10);
emaxHat ~ normal(0, 50);
ed50 ~ normal(0, 50);
sigma ~ cauchy(0, 2);
omegaE0 ~ cauchy(0, 2);
omegaEmax ~ cauchy(0, 2);

e0 ~ lognormal(log(e0Hat), omegaE0);
emax ~ lognormal(log(emaxHat), omegaEmax);

logResponse ~ normal(log(responseHat), sigma ./ exp(log(n) / 2));
}

generated quantities{
vector<lower = 0>[nStudies] e0Pred;
vector<lower = 0>[nStudies] emaxPred;
real<lower = 0> responseCond[nArms];
real<lower = 0> responseHatPred[nArms];
real<lower = 0> responsePred[nArms];

Individual predictions

for(i in 1:nArms){
responseCond[i] = exp(normal_rng(log(responseHat[i]), sigma / sqrt(n[i])));
}

Population predictions

for(i in 1:nStudies){
e0Pred[i] = lognormal_rng(log(e0Hat), omegaE0);// generate new e0
emaxPred[i] = lognormal_rng(log(emaxHat), omegaEmax);// generate new emax
}
for(i in 1:nArms){
responseHatPred[i] = e0Pred[study[i]] + emaxPred[study[i]] * dose[i] / (ed50 + dose[i]);
responsePred[i] = exp(normal_rng(log(responseHatPred[i]), sigma / sqrt(n[i])));
}

}
/////

Best regards

The issue contains a pasted Stan model for meta-analysis data and asks how to add inter-occasion variability. No repository file, test, or entry point is identified, and the desired completed change is not defined.