Ubuntu tmp folder is full with really old cache file, how do I safely delete them?

I've found that the Ubuntu server /dev/sda1 is full. there are really old cache files (named like 0.cacheVHfew stored in /tmp folder. I've checked the php.ini, it is using opcache.

How do I safely remove the really old cache file from /tmp?

Thanks!

I tried to restart the sudo service php7.3-fpm reload, but the really old cache files still exists in /tmp folder.