The ARPA provision is for waiving repayment of the Advanced Premium that would have been paid on behalf of your client. Not "the premium" but any supplemental amount paid on their behalf. That's part of the "affordability" part of the ACA = Affordable Care Act.

The 1095-A would be linked to the Sched C, along with any other premiums the taxpayer incurs for their new policy, to show it is allowed as deduction against the gross income of that business.

Then, if they fall below the 401% limit, they get to deduct the additional amount on the 1040 = Form 8962.

"It seems this is correct but why wouldn't it have been taken into account by the prior CPA?"

Not everyone knows what they are supposed to be doing. You might recommend amending the prior year(s).