You can buy another access key on learntomod.com: https://www.learntomod.com/sign-up/ The access key will be sent to the email you purchase with.
This access key you can buy on learntomod.com is a recurring 1-yr subscription and it's $29.99 usd per year. If you ever want to opt out of the automatic billing, email firstname.lastname@example.org and forward them your receipt.
Afterwards, you can login as usual to your learntomod account, then click the Account gear icon in the middle of the learntomod homepage, then scroll down until you see 'add time'. click that and enter the new access key.