Unfortunately, this cannot be customized easily as those fields are dynamically generated regarding the theme options selected and to our knowledge, there is no plugin that you could install to add this feature to your website. We think that this feature requires custom development work.
If you’re on a tight budget, we recommend you to require the services from Envato Studio freelancers (https://studio.envato.com/explore/websites-programming). This web platform gives you access to developers who have already experience with theme customizations, and for very competitive prices.
In case you choose to change this, we can point you to the bit of code to change.