Just re-enter the chrooted environment, as mentioned in chapter 6.4
chroot "$LFS" /tools/bin/env -i \
HOME=/root TERM="$TERM" PS1='\u:\w\$ ' \
/tools/bin/bash --login +h
The above command does not create a permanent environment, you enter the environment you created in chapter 5.
BTW: If you rebooted, you also need to do the parts mentioned in the NOTE at the bottom of the page.
Hope this helps.