<form><div class="col-7 header__auth"><input placeholder="Логин" class="header__auth__input header__auth__input--login"><input type="password" placeholder="Пароль" class="header__auth__input header__auth__input--password"><input type="submit" value="Войти" class="header__auth__input header__auth__input--submit"></div></form>

 CodeStr := 'document.getElementsByClassName("header__auth__input header__auth__input--login")[0].value="UnitDmitrovka";' ;
 Chromium1.Browser.MainFrame.ExecuteJavaScript(CodeStr, 'about:blank', 0);

				<form @submit.prevent="auth">
					<div class="col-7 header__auth"><input
							class="header__auth__input header__auth__input--login" v-model="authItem.login"
							placeholder="Логин"><input
							class="header__auth__input header__auth__input--password" v-model="authItem.password" type="password"
							placeholder="Пароль"><input
							class="header__auth__input header__auth__input--submit" type="submit" value="Войти">
              <!--      <a href="/forget-pass/" class="HomePage-forget-pass">Забыли пароль?</a> -->
                    </div>
				</form>