SQL Cast Mariadb Query - Add to output before exporting to variable

I'm trying to update a stats server due to Player ID formats being changed.

This is the starting values which will be queried.

MariaDB [hlxce]> SELECT * FROM `hlstats_PlayerUniqueIds` WHERE playerId = 562;
+----------+----------------+---------+-------+
| playerId | uniqueId       | game    | merge |
+----------+----------------+---------+-------+
|      562 | [U:1:18893661] | cstrike |  NULL |
+----------+----------------+---------+-------+
1 row in set (0.00 sec)

I butchered this together which at least matches the uniqueId but isn't updating the communityId correctly.

MariaDB [hlxce]> SELECT
    ->           hlstats_PlayerUniqueIds.uniqueId,
    ->           CAST(MID(hlstats_PlayerUniqueIds.uniqueId,6,-2) AS unsigned) + CAST('76561197960265728' AS unsigned) AS communityId
    ->           FROM
    ->           hlstats_PlayerUniqueIds
    ->           WHERE
    ->           hlstats_PlayerUniqueIds.playerId = 562;
+----------------+-------------------+
| uniqueId       | communityId       |
+----------------+-------------------+
| [U:1:18893661] | 76561197960265728 |
+----------------+-------------------+
1 row in set, 1 warning (0.00 sec)
MariaDB [hlxce]>

In short, I just want to ignore the 5 left characters ( [U:1: ) and the 1st character on the right ( ] ). So in this example I'd have 18893661 and from there, I simply want to add 76561197960265728 to it and export it as $communityId

If it helps this was the original SQL statement that stopped working.

MariaDB [hlxce]> SELECT
    -> hlstats_PlayerUniqueIds.uniqueId,
    -> CAST(LEFT(hlstats_PlayerUniqueIds.uniqueId,1) AS unsigned) + CAST('76561197960265728' AS unsigned) + CAST(MID(hlstats_PlayerUniqueIds.uniqueId, 3,10)*2 AS unsigned) AS communityId
    -> FROM
    -> hlstats_PlayerUniqueIds
    -> WHERE
    -> hlstats_PlayerUniqueIds.playerId = 562;
+----------------+-------------------+
| uniqueId       | communityId       |
+----------------+-------------------+
| [U:1:18893661] | 76561197960265728 |
+----------------+-------------------+
1 row in set, 1 warning (0.01 sec)
MariaDB [hlxce]>

EDIT****

To clarify
uniqueId ( without [U:1: nor ] ) + 76561197960265728
(18893661 + 76561197960265728) = 76561197979159389 
76561197979159389 = communityId

I've never really tried to manipulate data like this so my apologies if its blatantly obvious.

you can use SUBSTRING to extract the required string from uniqueId and then add 76561197960265728 to form communityId.

[U:1: => This constitutes of 5 characters, so SUBSTRING start position is from 6th character and then the extract length can be the entire length of uniqueId minus 5 character minus the ] i.e 1 which is at the end.

SUBSTRING(uniqueId, 6, LENGTH(uniqueId) - 5 -1)

Sample Query

    select playerId, uniqueId, game,
    cast(SUBSTRING(uniqueId, 6, LENGTH(uniqueId) - 5 -1 ) as UNSIGNED) + 76561197960265728 as communityId
from  players
where playerId = 562;

Outputs

Fiddle Demo