Istio 1.4.1 upgrade 1.5.x missing istiod by using helm

Greeting ! Our taget want to upgrade the istio to 1.6.x. But seem it need to upgrade to 1.5.x first. And I tried to upgrade istio 1.4.1 version to 1.5.x version by helm but missing the istiod deployment… what should I do ?
Could I using the istioctl command to upgrade the version again or install the istio on top current istio installation ?