It is too late for the 2019 tax year ...
Once you have set up your accounting method and filed your first return, generally, you must receive approval from the IRS before you change the method. A change in your accounting method includes a change not only in your overall system of accounting but also in the treatment of any material item.
Approval required.
The following are examples of changes in accounting method that require IRS approval.
• A change from the cash method to an accrual method
or vice versa.
https://www.irs.gov/pub/irs-pdf/p538.pdf
