Whenever you see the verb have in any of its forms ( have, has, having, had) be sure that the verb that follows it is in the past participle form.
They had walk to school should be had walked
We have see the show should be have seen
He has took the test should be has taken
Having ate, he went to school should be having eaten
She should have did the work should be should have done
VERB FORMS AFTER HAVE
have plus past participle