This is how I did it on macOS:
vim ~/.bash_profile # macOS 10.14 Mojave and older
vim ~/.zshrc # macOS 10.15 Catalina and newer (using zsh by default)
And added the following environment variables:
export ANDROID_HOME=/Users/{{your user}}/Library/Android/sdk
export ANDROID_SDK_ROOT=/Users/{{your user}}/Library/Android/sdk
export ANDROID_AVD_HOME=/Users/{{your user}}/.android/avd
Android path might be different, if so change it accordingly. At last, to refresh the terminal to apply changes:
source ~/.bash_profile # macOS 10.14 Mojave and older
source ~/.zshrc # macOS 10.15 Catalina and newer (using zsh by default)