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@KASHANICPA wrote:

 Appreciate it if you can please inform how to obtain additional depreciation allowance for 2018 assets if filing under 2019 tax returns.

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You need to amend the 2018 tax return to claim Bonus Depreciation for Qualified Improvement Property.   The extra depreciation does not go on the 2019 return; in fact, the 2019 depreciation would be zero because the full amount of depreciation should be in 2018.