How to get it?

You may build it. Or if you don't want to build the app yourself then just pull the right FAP file from latest release and put it to your Flipper Zero device by copying it to /ext/apps/Misc. After that you should be able to run it on your Flipper.

To pick the right FAP file you would need to know what firmware your Flipper Zero device is running:

FAP file name	Base firmware	Compatibility
totp_official-stable_fw.fap	Official Stable	Official Stable and any other firmware based on it
totp_official-dev_unleashed_fw.fap	Official Dev	Official Dev and any other firmware based on it, such as Unleashed, RogueMaster, Flipper-Xtreme, Dexv

If you are not so sure which firmware your Flipper is running try totp_official-stable_fw.fap first and then if it will not work for your then try totp_official-dev_unleashed_fw.fap.