There should be a page (wallet?) with a standard on chain Bitcoin address that you send funds to. It then adds it to your Lightning address.

Create an invoice and pay it from another Lightning wallet with enough funds to cover the invoice

You find your unique on-chain Bitcoin address on the ‘receive’ page of your Alby account.

You need to login on their web page and there is a huge receive button you can’t miss

DMing you

There are various options which are described here: https://guides.getalby.com/overall-guide/alby-lightning-account/how-to-top-up-your-wallet-balance