Himself is a reflexive pronoun that has the male object of a verb or prepositions that also appears as a subject.
"He did the job himself."
Hisself is an inappropriate word in English which is also deemed incorrect and should beavoided in official writings and documentations.
In official grammar rules, himself is the correct reflexive pronoun for a singular male person.
"The little boy learned to tie his shoes by himself."
Hisself is a regional variation you will hear in some spoken dialects.