Need help with some customisations

Hello,

I am using your plugin Rsilitech postcode availability and it has proven to be quite useful. However, I need help with some things. I will be obliged if you would help me out with the same. The issues are:
1. When a user enters the post code(we use pincode), they will either press the ‘Check’ button or, most likely, will press ‘ENTER’. But when I press enter after entering the number, the page refreshes. It is very important that the pin code be accepted by pressing ‘Enter’
2. While making a new code entry, I could not find any place to enter COD availability. Without it there can be no COD facility.
3. Two design-based support needed:
Please make the check button next to the field
Can I have a button with non-round corners?
The check availability box is not aligned right like the rest of the page(refer photo: https://ibb.co/6bnCBMQ ). Can you please make this happen?

Following changes have already been done.

/*check availability title making short */
h3.rsilitech__title.js-title{
font-size: 22px;
}
/*height of pin code enter box and button box*/
div.rsilitech-group{
height: 130px ;
width: 170px;
}

FOR TESTING PURPOSE, THE ONLY PINCODE ACCEPTED IS 226006

The page I need help with: [log in to see the link]