Since Apple announced iOS 15 many people have been looking to install it on their devices, thankfully installing the beta is easy simply go to the OTA profile*, once you have the profile simply install it onto the device and tap install here.
Before any attempts of downgrading are made make sure you backup your data like Photos and stuff to iCloud or locally to your PC before proceeding, note that full Backup option available in iTunes and iCloud won’t work if you try to restore a backup made from a newer firmware onto an older version.
Step 1 Download the current version of iOS 15 Beta firmware profile directly on your device typing your passcode when prompted.
Step 2: Click install
Step 3: Wait for the profile to download and click restart when prompted
Step 4: Wait for your device to restart and the software update to install
Once complete you will now have your device on iOS 15 Beta.