Can't use susbdomain as email-address

Can't use susbdomain as email-address

Hello,
I would like to know how to add subdomain to zoho mail for email addresses. Currently i'am using a free trial Mail premium and i will subscribe as soon as i know how i can add subdomain . I understand that in a free trial you can't add more than 1 domain so i will delete my already existing domain and replace it by subdomain .  For example my main domain is division-cash.com and i want to use notaire.division-cash.com so my email address will be xxxx@ notaire.division-cash.com. Please provide me step by step guide since i'am not familiar with subdomain creation. My domain provider is namecheap and i don't know how to setup these stuff both side namecheap and zoho mail. 

 Thanks in advance For your help.