How to access Apple Store account from PC?

Hi.

My son's iPad Air is out of action for the foreseeable future due to a cracked digi screen - see other thread!

Unfortunately this won't stop his Apple Store account being debited for various Apps he's subscribed to...

How can he access his account from a home PC? He has all the info (he thinks...) such as username and password and stuff, but how do he do this without having his knackered iPad in use?!

Thanks.