So I'm trying to build LFS 12.1 and recently ran into an issue where I must have messed up an install on Chapter 6. Initially when I was in the chroot shell I kept getting command not found for 'sed'. I must have messed up this install or accidentally skipped it. I only resolved this by reverting to a snapshot I had before this. Now that is resolved, I am currently on 8.5.1. Installation of Glibc and getting the same thing with the 'patch' command running 'patch -Np1 -i ../glibc-2.39-fhs-1.patch'. I resolved this by manually installing patch within the chroot shell. What is the proper way to reinstall this if it happens again and then reload the shell so it picks up the new installation? I am somewhat new to LFS but not sure how to go about properly resolving this.

Complicated fixes like manual installs out of sequence may work in the short term but you invariably run into the sand further down the line. I don't think there is any future in this particular build. In your place, I would clear the partition, except for /sources, and start again from Chapter 5.

Don't be downhearted; we've all had to do that sometimes and it's especially common on a first LFS build.