Subdomain TLS for existing Let'sEncrypt TLS cert

Just want to ask if I have followed the echo AutoTLS recipe cookbook for my domain ( The TLS provided by Let’s Encrypt will be for 3 months by default. But if after 1 month having the certificate, and i want to add few subdomains (eg., will TLS auto update the TLS cert given previously to also have the subdomain? or i have to wait for the whole 3 months term to finish only then i can apply TLS for subdomains?