Reduce MySQL request time with Codeigniter - php

Question

I use Codeigniter 3.1.11 and have some code which makes one big query to MySQL with an array. The time of a query with a limit of 30000 is about 9 seconds.
How can I reduce the request time? Maybe by using some indexes on my table, or do you know another method? If I need to use indexes, what indexes would I need to use and how can I use these indexes in my query on Codeigniter?
Code from model:
function rows_update() {
$query = $this->db->order_by('rating', 'DESC')->get_where('members', 'game_rating_and_balance_update_last_time <= now() - INTERVAL 1 DAY', '30000', '0');
$arrUpdateBatchData = [];
while ($row = $query->unbuffered_row('array'))
{
// some code here
$arrUpdateData = [
'UserID' => $row['UserID'],
'game_vault_balance' => $new_game_vault_balance,
'game_available_balance' => $new_game_available_balance,
'rating' => $rating_member,
'game_rating_and_balance_update_last_time' => date('Y-m-d H:i:s')
];
$arrUpdateBatchData[] = $arrUpdateData;
if (count($arrUpdateBatchData) > 500)
{
$this->db->update_batch('members', $arrUpdateBatchData, 'UserID');
$arrUpdateBatchData = [];
}
}
//update last items
if (count($arrUpdateBatchData) > 0)
{
$this->db->update_batch('members', $arrUpdateBatchData, 'UserID');
$arrUpdateBatchData = [];
}
return;
}
Raw query to MySQL with update_batch (I simply write only one row from an array):
UPDATE members SET game_vault_balance = CASE WHEN UserID = '9915075' THEN 803.60516004772 ELSE game_vault_balance END, game_available_balance = CASE WHEN UserID = '9915075' THEN 4.1253850908788 ELSE game_available_balance END, rating = CASE WHEN UserID = '9915075' THEN 0.24 ELSE rating END, game_rating_and_balance_update_last_time = CASE WHEN UserID = '9915075' THEN '2020-07-24 22:00:36' ELSE game_rating_and_balance_update_last_time END WHERE UserID IN('9915075')
Table structure:
CREATE TABLE `members` (
`id` int(10) UNSIGNED NOT NULL,
`UserID` varchar(64) NOT NULL,
`telegram_id` varchar(64) DEFAULT NULL,
`first_name` varchar(64) DEFAULT NULL,
`last_name` varchar(64) DEFAULT NULL,
`language` varchar(64) DEFAULT NULL,
`currency` varchar(64) DEFAULT NULL,
`status` varchar(64) DEFAULT NULL,
`rating` varchar(64) DEFAULT NULL,
`game_vault_balance` decimal(32,8) DEFAULT 0.00000000,
`game_available_balance` decimal(32,8) DEFAULT 0.00000000,
`game_rating_and_balance_update_last_time` datetime DEFAULT NULL,
`updated` datetime DEFAULT NULL,
`created` datetime DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Indexes of this table:
ALTER TABLE `members`
ADD PRIMARY KEY (`id`),
ADD UNIQUE KEY `UserID` (`UserID`) USING BTREE;
AUTO_INCREMENT for the members table:
ALTER TABLE `members`
MODIFY `id` int(10) UNSIGNED NOT NULL AUTO_INCREMENT;
COMMIT;