Editing plugin

Hello I’m trying to edit the plugin AWPCP. I’m NOT trying to do CSS editing, I understand that part. The question might be more general WordPress plugin related and not specific to AWPCP therefore I’m posting here.

What I’m trying to do is for example there’s an input field with title “how much” but I would like to change it to say “dollars”. How is this done? Really confused because my traditional thinking tells me to look for HTML file but I know WP is php.

Also the backed admin for the plugin doesn’t give me the option to change that title. Isn’t there another way of doing this? Is this not possible?

Thank you
Brian