Hi,

Extend the "web.FormView" template and add a new button.

<templates xml:space="preserve">

   <t t-inherit="web.FormView" t-inherit-mode="extension">

       <xpath expr="//button[contains(@class, 'o_form_button_create')]" position="before">

           <button type="button" class="btn btn-primary history_btn" id="history_btn"

               t-on-click="buttonClicked">

               <span>NEW BUTTON</span>

           </button>

       </xpath>

   </t></templates>

Need to create a JS file inside static/src/js directory(eg :static/src/js/form_button.js)

import { patch } from "@web/core/utils/patch";

import { FormController } from "@web/views/form/form_controller";

patch(FormController.prototype, {

    setup() {

        super.setup();

    },

    buttonClicked() {

    // Add your code

    },

});

Hope it helps