Translation:Dolaşırken onu gördüm.
You have to put onu after dolaşırken if you want to mean that you saw her, him, or it. I don't think that "onu dolaşmak" makes sense. Does it? I think "ben onu dolaşırken gördüm" might mean "While I was walking around him/him/it, I saw". Anyway, even if it did, that isn't the right translation of the sentence.
It should be "Ben dolaşırken onu gördüm." The subjects for 'dolaşmak' and 'görmek' are the same, so "ben" is listed at the beginning of the sentence. Otherwise, it leaves the subject of "dolaşırken" to be really vague and confusing. :)
ok thats understandable but the duo translation didn't use ben as another choice of translation at all
It does if you put it at the beginning of the sentence :)
"o" needs the accusative suffix (-nu in this case). It's the direct object of the sentence. Every time you use a pronoun as the accusative part of the sentence, it needs the accusative suffix.