How Do I attach code to a button to be used in shopify theme

Hello 

Im working with a developer and we wanted to know the best way to do something on shopify please

I would like to create a custom programming code which allows my shopify  customers to enter text into the product options area when selecting a product , that inputted text is taken off of shopify to go and create/get a QR code (image) ,and then that new QR Code (image) comes back to shopify and is uploaded into the product customizer app). we will use an api to generate QR code. Its just getting info from shopify, then going to create code, and return it back into the shopify / product customiser app

What is the best way to do this? Can i attach custom code to a button? and display that button in my product options area 

Is it best to use an api to extract the data from shopify, or would i have to use a DEv Kit and liquid programming langue to be able to add a button to shopify which has my programming code on it or Do you know the easier way to achieve this? I want my custom to entre text, that creates a qr code, and then that QR code is uploaded to my product customizer app 
please do let me know and Thank you for reading!

@GEORGEBYRNE93

sorry for any issue can you please share us screenshot for that issue?