Override PHP file to add custom buttons in editor

Hello
I’m a developer, writing on behalf of my client.

We bought this plugin and got that it’s a nice plugin to use. But we need to add “Quote” button on the editor.
When I’ve come to create a ticket here, I see that here in this form buttons are “Quote, numbered list” etc.
Also here options like “Visual and Text” editor.

My first question : Is there anyway to get in our website the same form buttons and editor in here?
otherwise, I’ve got that I’ve to customize the file in “dw-question-answer-pro/inc/Editor.php” because I am not successful to overwrite Editor.php file from child theme, I added style file correctly but PHP file is not working, i’ve added code below which is working here : 
https://taxationistheft.info/dwqa-ask-question/
`,
{
name: “heading”,
action: SimpleMDE.toggleHeadingSmaller,
className: “fa fa-header”,
title: “Heading”
},
{
name: “unordered-list”,
action: SimpleMDE.toggleUnorderedList,
className: “fa fa-list”,
title: “Unordered List”
},
{
name: “quote”,
action: SimpleMDE.toggleBlockquote,
className: “fa fa-quote-left”,
title: “‘.__(“Quote”, ‘dwqa’).'”
}
`
My second question is : how can I overwrite PHP file from theme ?
Looking forward to getting a proper reply. If needed I can get token and connect plugin to Evanto

Please let me know the answers to my question.

Thanks