Help and guidance for How to react to messages using High Level.
To react to messages, create workflows in high level with the desired reaction

Choose which reaction you want to add for that workflow. People usually have thumbs up for one workflow, thumbs down for another, and so on.
Leave the trigger empty since you will be triggering it manually later
Make sure you allow re-entry in the workflow since you want to react to people’s messages multiple time.
To use it, you can trigger that workflow from the conversation view like this

Then choose the workflow you created and it will add the reaction you need
You can trigger these workflows from your iPhone/Android as well using the leadconnector/GHL app on either platform.