Use .modify() function to update the value of the secret

var service = new SecretService();
var option = new SecretUpdateOptions
   {
       Key = "YOUR_UPDATE_SECRET_KEY",
       Value = "YOUR_UPDATED_SECRET_VALUE",
   };

// Update a secret value by secret key
var updated_secret = service.Modify(
    name: "YOUR_SECRET_KEY",
    updateOptions:option
    );

// Update a secret value by secret key and a specific environment name
var updated_secret = service.Modify(
    name: "YOUR_SECRET_KEY",
    environmentName: "YOUR_ENV_NAME",
    updateOptions:option
    );