Arsenal won the FA Cup later that season, before finishing eighth the following campaign.
They came fifth in 2021-22 but have since become title contenders, finishing second for the past two seasons.
Arteta said his early tasks as manager included improving the “culture” at the club.
“What I did was basically ask, through somebody I employed, to give me their opinion of how they feel to work in this football club,” explained Arteta, whose side travel to Crystal Palace in the Premier League on Saturday.
“It was clear that it had to be changed.
“[It was pivotal] because that was the roots of the football club. If those roots were damaged at that level, there was nothing to build without that.
“So in the first season, we had to put the energy and big decisions into making sure those roots were clean and were in the right context and in the right place to be able to create and build what we wanted to build.”