How to add a text box to product listing from a purchased template that has used Json not liquid.

[Lizabefy]

Hello all 
I am trying to add a custom text box code to my product listing. My business is an online fabric store and I would like to add a text box for custom print names and a drop down box for scaling. My varients I have already used to cover my fabric and vinyl bases I offer.

I have tried following advice and blogs and trouble steps on how to add it but the code either doesn't work or it doesn't pull the data through to the checkout when placing an order. 
I keep seeing 'liquid' everywhere however my shop theme that I purchased created by someone on etsy, has all the templates made in Json. Things that people are are screen shotting and sayin 'insert here' aren't there. 

I am clueless with how to code and really struggling. 

Please help ❤️