First, ensure that developer options are enabled on the device
SettingsMy Fire TVAboutFire TV Stick HD until No need, you are already a developer. message appears.Return to the My Fire TV screen (clicking return once should get you there)
Developer options should now be just below About
Open the Developer options and you should see the following menu items:
ADB DebuggingInstall unknown appsEnable ADB Debugging
https://learn.microsoft.com/en-us/java/openjdk/download#openjdk-21
Nothing special here of note, follow the basic wizard/installer and install the latest/desired version of an OpenJDK
https://developer.android.com/studio/index.html#android-studio-downloads