Hello,
For that, you need to remount the system partition.
To make that you need to make it through ADB.
First, make sure that you have the ADB capability activated.
In the Windows/Linux command prompt type the below ADB commands:
adb start-server
adb root
adb disable-verity
adb reboot
After the system reboots.
adb start-server
adb root
adb remount
After performing those commands, you should have access to root directory.
Hope this could help you.
Best regards,
Diego.