As Terry mentioned, they only filed one year with an incorrect method so Form 3115 does not apply.

File the current year as it should be.  If the client is okay with amending 2022, amend that when you have time (not a super hurry).

With that being said, you may need to figure out 2022 first.  Unless they elected out of Bonus depreciation in 2022, I suspect that most or all of the equipment will have been fully depreciated in 2022 so it is likely there won't be any further depreciation in 2023.  But if they will be using Section 179 for 2022 and it creates a loss, the unused Section 179 would be carried forward to 2023.