Short Answer 
To install an APK on your LG Smart TV, first insert the USB drive containing the APK file. Then download and open ES File Explorer from the LG Content Store, navigate to your USB drive to locate the APK, and click to install it after confirming compatibility with your TV model.
Step 1: Insert the USB Drive
Begin the installation process by inserting your USB drive, which contains the apk file, into the USB port of your LG Smart TV. Make sure the USB is properly connected; this is essential for the TV to recognize the device and access the files stored on it.
Step 2: Install ES File Explorer
Next, download the ES File Explorer application from the LG Content Store on your TV. This file management tool will help you navigate through the files on your USB drive and locate your apk file easily. It’s important to ensure that you have this app installed as it facilitates the installation process of applications on your smart TV.
Step 3: Locate and Install the APK
Open the ES File Explorer and go to the ‘Local’ option, then select ‘USB’ to access your USB drive. Find the apk file you want to install and click on it. A prompt will appear asking for confirmation; simply click the install button to proceed with the installation. Make sure the apk file is compatible with your LG TV model to avoid any issues during installation.