Hi,
Sorry, I am not able to replicate your issue.
The select image button is there.
Please see my screen-cast.
https://screencast-o-matic.com/watch/cbhnVkXqgc
Please use the following troubleshooting steps.
Check your Child theme.
1) If you are using a child theme, you can check whether it’s an issue with your child theme by activating your Hueman Theme.
2) Clear any cache plugin’s cache content and browser history before re-visiting your customizer.
Check your software version.
1 ) Check if you are using latest Hueman and Hueman Addons plugin, Update them if you are not using latest version.
Next step is to check for plugin conflict.
1) If you are using a server cache or cache plugin, please clear it’s cache content and disable caching via it’s settings.
2) Proceed to disable one plugin at a time, clear browser history and re-visit your customizer. Check if it’s working properly.
Do this until you find the plugin that’s causing this issue, please replace with an alternative plugin.
Thank you