T2 Security chip
can the T2 Security chip be installed in my MacBook air (purchased June 2017)?
MacBook Air 13″, macOS 10.15
Oh, that's not true at all. If you should lose your Mac, follow these instructions: If your Mac is lost or stolen - Apple Support. Note that you have to enable "Find My Mac" before you lose it, so if you haven't done that yet now would be a good time.
To learn how to do that read Set up Find My Mac. Do it now.
Apple offers a number of additional steps you can take to ensure the security of your Mac so that if it becomes lost or stolen it becomes literally impossible to use:
Encrypt Mac data with FileVault - Apple Support
How to set a firmware password on your Mac - Apple Support
Although it's not strictly related to device security, consider protecting your Apple ID with two-factor authentication:
Two-factor authentication for Apple ID - Apple Support
Taken as a whole, those precautions preclude unauthorized use of your devices or your Apple ID credentials.
Finally, unless you maintain a backup of the information on your Mac, you will lose it... eventually, regardless of whether it should become lost, stolen, damaged, or simply inoperable. To learn how to use Time Machine please read Back up your files with Time Machine on Mac.