For those unaware, the Developer Preview is a programme for app developers to give them an early look at the upcoming features so that they can make their apps compatible and build for the next version of Android.
Google will roll out the beta version of the same to public later this year, but if you cannot wait to get Android 12 operating system for your phone then this is what you need to do:
Click on this link https://flash.android.com/preview/dp1 to to download DP1 (developer preview) flash tool
Click on Get Started
Before that make sure to download Android USB driver
Enable Developer Options Menu by tapping on the Build Number option 7 times
Enable USB debugging by toggling the USB debugging setting within developer options menu
Enable OEM unlocking by toggling the OEM unlocking setting
Connect your phone with your PC
On the webpage click on Add New Device, then select the device model and click on Connect
Select your connected device on the browser
Choose the Developer Preview build from the list
Click on the Install button
Reboot when done
Readers must note that only a handful of phones support the developer preview of Android 12. These are Pixel 3 series, Pixel 3a series, Pixel 4 series, Pixel 4a series and Pixel 5.
Also, another thing to keep in mind before going ahead with this process is that since the operating system is in a developer preview stage right now it is likely to be unstable and may cause trouble for daily use therefore keep a backup of all your personal data.