The tense used in "During..."

Dear teachers,

I would like to ask wheter the use of the past perfect, instead of the past tense, is correct if the action had been taken place for several times in the past.

"During the reporting period, ABC had assisted (or assisted) in (the) preparation of the promotion activities of EFG."

Thank you.

(not a teacher)

You could use either one. I'd use simple past.