File a 5329 for 2017 for any distribution that did not happen, with a request for waiver. (Not applicable if the decedent did the appropriate RMD for 2017) 

File a 5329 for 2018 for any distribution that did not happen for 2017? + 2018, with a request for waiver.

File a 5329 for 2019 for any distribution that did not happen for 2017? + 2018 + 2019, with a request for waiver. 

Why was there no catch up done when it was allocated in 2019? That is possible the one that might not be waived, but ask anyway. 

The 5329 can be filed all by itself and mail to the appropriate service center to be opened and processed someday.