In English this is a bit ambiguous, so I'll explain a little. The participle is when the subject is being acted upon, and not when it's doing the acting. For example, in 'I ate the bread' ate is past tense. In 'The bread was eaten' eaten is the participle. Obviously the bread isn't doing the eating in the second sentence. Some English verbs aren't so clear on this. For example, 'He was hired' versus 'We hired him, hired is the same. There's no hire'-en'.
Like most forms of verbs in Reisu the participle is formed with a suffix -ri. So 'The bread was eaten' is 'Inoko amulari'.
This suffix is only needed if there is no passive voice clause. 'Ba' forms the passive voice clause, similar to the word 'by' in English. So 'The bread was eaten by me' is 'Inoko amula ba ei'. The suffix -ri is not needed. It's clear that the subject is being acted upon by the verb because of the presence of the phrase 'ba ei'.
'Inoko amulari ba ei' may still be said if 'ba ei' is an afterthought. Otherwise it sounds redundant.