How did these many people you speak of that voted in a registered voter's place that was dead, do it?
I'm not aware of all of the possible methods, but some should be obvious, even to you. And you should bear in mind that one person can perform this fraudulent act multiple times in multiple places
One method is to determine the name and last known address of a recently deceased adult, determine the voting precinct for that address, go to the polling place of that precinct and vote. With little or no voter ID required, signature verification absent...the vote is counted.
Another is to obtain a ballot that was mailed to a deceased person from one of the family members.
Explain how it could be done.... how did they know a voter was dead,
Public records, obituaries, news stories, word of mouth...
how did they have his signature and address to request a ballot, and where was the ballot mailed to by the election office, so this fake person could get it and fill it out and the envelope with signature etc. out?
See above. And there were many unrequested ballots mailed out. In some cases, multiple ballots were sent to the same address.
One person, a Trumpet, requested a ballot for his mother who had just died so he could vote in her place, and voted in person as himself... but he was caught, by the checks in the system...and charged with a felony.
I haven't claimed that only Democrat Party members cheat. Besides, had a similar incident occurred involving a Democrat Party member, it may have gone unpunished since the Democrat Party controlled the counting and verification procedures.
Do you know the procedures in each contested state on how they update their voter rolls and remove the dead and remove felons from their active voter rolls?
No. I'm not aware of all of the procedures even in my home state. And I've read that HR1 (a partisan Democrat Party created abomination) proposes to limit the purging of voter registration rolls in all states. In other words, the Democrat Party wants to maintain existing voter registration rolls containing the names of INELIGIBLE VOTERS. I wonder why! Duh!
It's not easy to vote in the name of a dead person with all of the checks in place...I'd say closer to damn near I.possible.
As you may have read in the article I previously linked, it is quite possible to impersonate a registered voter, dead or alive. Then again, you may not have bothered to read it through.
It didn't happen....it can't happen...
You should revise that claim as it is clearly lacking in logic.
...and if it did happen,

it would be so so minimal that it would NOT come close to changing any result of any presidential election.
(1) You're contradicting the beginning of the sentence you made.
(2) You have no idea how minimal it would be.
(3) You have no idea how close any one race would be in any one precinct.
Bottom line:
You're blowing a lot of hot air with no significant truth in your words.