Question

что неправильно собрала, вроде где то напутала, а понять не могу
The concert by was watched thousands of people.

Answer 1

The concert was watched by thousands of people. By не там где надо стоит

Answer 2

The concert was watched by thousands of people.
Страдательный залог -порядок слов-подлежащее,сказуемое,предлог (By-кем?),дополнение.