Move column to another table by reducing?
You'll need to do it in several steps:


Add the column to the store (I'm not sure what the type is, maybe it's something else):

ALTER TABLE store ADD COLUMN location VARCHAR(50)

Populate it, based on the most prevalent location of the employees. I'm not entirely familiar with MySQL syntax but the query should look something like this:

UPDATE store SET location = locations_by_storeid.location
FROM store INNER JOIN 
(SELECT storeid, location,
  ROW_NUMBER() OVER(PARTITION_BY storeid ORDER BY COUNT(*) DESC) row_number
  FROM employee
  GROUP BY storeid, location) locations_by_storeid
WHERE store.id = locations_by_storeid.storeid
  AND locations_by_storeid.row_number = 1


The subquery (locations_by_storeid) lists all locations for employees on a certain storeid, and we take only the most frequent one (the one with row number 1) as per your requirement 2.
Now we can remove the location from the employee:

ALTER TABLE employee DROP COLUMN location