After you have purchased an eSIM, you should have received an email to get your eSIM QR code.
You will be able to manage your eSIM from there including TopUp, rental extension etc...

①When you receive the email, following email, please click "Get your eSIM QR code".

②The button will lead you to the following page.
You will be able to check your usage, make a TopUp and extend the rental period.