On many distros, getting multilib support is very straight forward. For LFS, there is a version that provides multilib support, from normal binary execution to compiling 32-bit software from the supplied toolchain. The guide is called Multilib LFS, or MLFS. It can be read here. If you haven't built LFS with MLFS or built in multilib support already, then you will need to start over.
The same principles of compiling for 32-bit in that book will also apply to this book as well. If you haven't already, read Important Information to check what basic principles still apply in this book when targeting 32-bit.
Furthermore, read Which Instructions to Follow to find out which instructions to follow.