If you are filing Form 3115 to correct it, you enter a "481(a) Adjustment" as an "other" expense.

On the Asset Entry Worksheet, you would just enter the amount of Bonus depreciation taken 'last year', so this year's depreciation will show up as zero.

It would not show up on Form 4562.

Personally, I think it would be easier to amend 2018 than to file Form 3115 with 2019.