The below appears at first to be a bad mirror DNS error, but if you've ruled that out you just need to clear your broken yum cache and things will be good.
yum update
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: centos.01link.hk
* extras: centos.01link.hk
* updates: centos.01link.hk
http://mirror.worria.com/centos/7.8.2003/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not........