Change what a Button sends to server [closed]

I need to change the Information on a site, i have to login to my already and still existing account with my phone number but the site doesnt officially support my Region anymore if i try to login, the Textfield where my phone number has to be written, has a fixed “+XX” region code which is different to mine…

Hello, a few years ago i saw a Tutorial where someone explained how to Change the Price Value of a Shoppingbasket. So he added as example 1x eBook with a price of 1,99$, then he went to the basket, goes to payment and wenn the “Final”, “Pay Now” Button came he did somethin with a tool which i suddenly forgot the name of -.-‘…so he pressed the Button and then changed the price which gets send to PayPal i think it was, then the PayPal Payment Window opens with a price of 0,01$…so i dont want to do that exactly but ive registered on a webpage a few years Ago, I used to be able to register with my regional cell phone number, which is unfortunately no longer the case. However, I can no longer enter my cell phone number for verification to log in because the text field has a fixed region code (“+XX”). I would like to circumvent this by using the method described at the beginning and sending my cell phone number and region code to the server so that I can at least log in. I’m also interested in the process after thinking about it.

I hope my English isn’t too bad and someone can help me with my problem.

Regards