mysql> create table StringToDateDemo
   -> (
   -> YourDate varchar(100)
   -> );
Query OK, 0 rows affected (0.49 sec)

mysql> insert into StringToDateDemo values('10/27/2018');
Query OK, 1 row affected (0.11 sec)

SELECT  STR_TO_DATE(yourColumnName, '%m/%d/%Y')
   from yourTableName;

mysql> SELECT  STR_TO_DATE(YourDate, '%m/%d/%Y')
   -> from StringToDateDemo;

+-----------------------------------+
| STR_TO_DATE(YourDate, '%m/%d/%Y') |
+-----------------------------------+
| 2018-10-27                        |
+-----------------------------------+
1 row in set (0.00 sec)