There are a couple of ways to do this. Like most things, there is an easy way and a harder way. The choice is yours.
The harder way is to open each affected document, one at a time, and change the FAA (and/or owner). You may want to even re-route the document for approval if necessary to formally acknowledge the change in release authority or ownership. If this isn’t necessary, I would choose the easier way which is to use Data Editor and follow the step-by-step instructions in the linked document. I would encourage only searching for either the Document Owner or the Final Approval Authority one at a time in case there are documents for which the affected user is not both.
https://downloads.waypointglobal.com/downloads/DMSDE-UsingSuiteDataEditorToChangeDocumentOwner-FAA.pdf
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