Pyinstaller produces a binary depending from the python you used to build it. So if you use python 2.7 64 bit it is not possible, as far as I know, to produce a 32 bit executable. This is because Pyinstaller archives all modules and their dependencies (dlls, pyds etc..) which are 64 bit due to the python install.
As already said it is better, because of cross compatibility issues, to build 32-bit binaries.
Probably you can specify more your question.