How to fix "EXT4-fs (sda1): re-mounted. Opts: errors=remount-ro"
It's not an error, it just tells you that the partition /dev/sda1 has been remounted with the mount option errors=remount-ro. It's nothing you need to worry about. It may happen e.g. during a normal system startup if /dev/sda1 is your root partition.
The mount option means that the system should mount the partition read-only if an error occurs to minimize further damage or data loss and is used by default.