Support is not helping to resolve the issue. To all my questions the answer is the same - no, you can't do that. Careful, if you need to add a couple of custom fields - this theme is not suitable for you. It has poor customization.
Author response
Hello,
Custom fields: You should add your own custom fields in Fields Manager
If you want to customize, you have to go to source code
Please send us a support ticket here: https://apusthemes.ticksy.com/
Supporter will check and help you
Best regards!