According to the Apple Device Support Reference Materials, the steps to put an iPhone in recovery mode are:
* Plug your iPhone in to your computer using your USB to Lightning cable1.
* On a Mac with macOS Catalina or later, open the Finder. On a Mac with macOS Mojave or earlier, or on a PC, open iTunes1.
* Quickly press and release the Volume Up button, then quickly press and release the Volume Down
* button, and then press and hold the Side (or Power) button until the recovery mode screen pops up12. It won't happen instantly, so hang on for at least 15 seconds or so before you try it again2.
* Locate your device on your computer and choose the option to Update or Restore1.
These steps apply to all iPhones manufactured since 2017, including iPhone 8 or later, iPhone SE (2nd and 3rd generations), and iPhone 12 or later2. For older models, such as iPhone 7 or earlier, the steps may vary slightly1. References: 1: If you can't update or restore your iPhone or iPod touch - Apple Support 2: How to put your iPhone or iPad into recovery mode | iMore