I need to find update for canon MX340

Well, we don't know what MacOs you have and that makes a difference.

If you have macOS 10.13 or older, check for updates in the Mac App Store. If you have macOS 10.14 or higher, do System Preferences > Software updates:

If Canon have sent Apple an updated driver, those are the two places to look.

Otherwise go the the Canon support site and enter your printer's model number. Easy.

https://www.usa.canon.com/internet/portal/us/home/support/details/printers/support-inkjet-printer/mx-series/pixma-MX340/pixma-MX340?tab=drivers_downloads

I'd start with Canon...

https://global.canon/en/index.html