Finding entity/webform fields in the database
I used a query similar to this to help me find a list of tables and columns I needed to update:

SELECT DISTINCT
    table_name, 
    column_name
FROM
    INFORMATION_SCHEMA.COLUMNS 
WHERE
    column_name LIKE '%user%_target_id'
    AND (table_name LIKE 'field_data_field%'
    OR table_name LIKE 'field_revision_field%')


It's not ideal, and it still missed a couple tables.

I put the resulting list of tables and columns into a Python script and generated the SQL update statements I needed to run.

There is probably a better way to do it.