Need help expanding reach + fixing high frequency in a CBO Advantage+ Sales campaign

I’m running a CBO Advantage+ Sales campaign in Korea and could use advice on reach expansion / frequency fatigue.

For placements, I’ve excluded Audience Network and Messenger (we’re confident they don’t perform for us). Other than that, the setup is mostly Advantage+, with one constraint: minimum age is 20+.

From December to February (3 months), we spent about ~$91.0K in total, and our current daily budget is ~$2.1K–$2.8K/day

At this spend level, frequency has climbed a lot — cumulative frequency from Dec to Feb is around 5.48. Even when I rotate creatives with completely different angles and formats, CAC keeps rising.

So I’m assuming the audience is getting saturated, and I’m debating whether I should start a new CBO campaign from scratch.

In situations like this, what do you usually do to improve reach / reduce frequency in an existing campaign? Any tactics that work well before restarting with a new campaign?