odoo-survey-addons/survey_input_template_custom/templates/page.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

  <template id="page" inherit_id="survey.page">
    <xpath expr="//button[@t-if='last']" position="replace">
      <button t-if="last" type="submit" class="btn btn-primary" name="button_submit" value="finish">
        <t t-if="survey.submit_btn_label">
          <span t-field="survey.submit_btn_label"/>
        </t>
        <t t-else="">
          Submit survey
        </t>
      </button>
    </xpath>
  </template>

</odoo>