Change quantity dropdown to textbox

Hi,
I ‘m using this plugin and I need to change the selectbox to textbox so that anyone can donate as you wish.
Here is the form .

https://peachsneetfeet.com/sponsoring-shoes/

See here ,two donation form have been shown and every have selectbox.

I need to convert it to the textbox .

How can it possible ?
waiting your response please.

https://wordpress.org/plugins/shopp/