how can I update my scanner to work with Catalina?

You could do worse than install the driver and firmware from HP which is labelled as being provided for macOS 10.15

It's easily found on Google.

The linked driver software was updated a month ago, in November, and the firmware in July.

You are not very patient are you, only waiting two minutes before demanding an answer.

You are not speaking to anyone from Apple here, only users like yourself

and we will respond when we think we may have an answer to your problem.

Have you been to the HP Support website for your printer, you should have gone there first,

click on this link,

https://support.hp.com/gb-en/drivers/selfservice/hp-envy-5540-all-in-one-printer-series/5447939 make sure the operating selector is set to macOS 10.15.

There are three downloads for you click on the + buttons

and download each, when you have downloaded them then install/ run them

and see if your scanner will operate.

It may also help to reset your printing system,

Reset the Mac printing system to solve a problem - Apple Support