How you renew your subscription to customer

Hi, I am making subscription in the sandbox paypal, after successfully tested the subscription, I found out that how can i renew the subscription for my customers example when one of my customer his subscription was expired how to let him renew his subscritpion do i need to create another subscription button then to let him press the subscrition button,same what i did for making his first subscription…please i need help for this.

Thank you in advance.