The passive is usually considered complicated for many students. Especially, the conversion between tenses other than present simple or past simple is difficult for most students, and they need to have more practice or see more examples.
This grammar guide summarises the passive constructions briefly in one-page PDF worksheet. It includes the way passive is formed, the basic rules of passive voice, some passive reporting structures and also a table for forming passive construction in different tenses.
You can study or revise passive constructions on the first page. Try to elicit the form, rules and the conjugation of passives in different tenses or forms. The other option is just giving it out as a grammar reference for students.