Right. Gotcha. If the "J. Doe1" multiple choice choices are sufficiently restricted, this is pretty easy. Add a field to that table for each field you need to change.
So, you have a [Reviewer] field with values like "J. Doe1", create [Reviewer (User)]. Make it a Formula - User field type. Write a long IF or CASE formula** to map your bad data onto good data, such as:
Case([Reviewer],
"J. Doe1","John Doe1",
"J. Doe2","John Doe2",
etc)
Where the first value in each pair is the exact multiple choice text string and the second value is the exact user name you want to change it to.
And then anywhere that you need QB to operate on this value as a user value, have it use the [Reviewer (User)] field instead of [Reviewer] .
** Or create a lookup table to map these values (this is probably your preferred approach if you have a lot of these paired fields to which the same mapping should be applied, or if you're going to continue to use [Reviewer] as your data-entry field going forward). Or, if the multiple choices were created with a single consistent pattern, this could be single line of formula if you're lucky.
