error message how to fix this?

-- url of the page with the problem -- : www.5gtv.com.tw
-- HikaShop version -- : 4.2.3
-- Joomla version -- : 3.9.16
-- PHP version -- : 7.3
-- Browser(s) name and version -- : safari
-- Error-message(debug-mod must be tuned on) -- : The HikaShop user synchronization plugin has been either removed or disabled from the website. It is a critical part of HikaShop and should not be disabled if you're using HikaShop on your website.Please enable that plugin via the Joomla plugins manager and then logout/login from the backend.

I have error so re- install system now.
But has error message ~

The HikaShop user synchronization plugin has been either removed or disabled from the website. It is a critical part of HikaShop and should not be disabled if you're using HikaShop on your website.Please enable that plugin via the Joomla plugins manager and then logout/login from the backend.
I need to enable which one plugins or install ?

I fix OK~ don't need to support now.
thanks