Mysql – thesql index on varchar and date field for improve query speed of select and insert query

CREATE TABLE IF NOT EXISTS `gsm_smslog220717` 
(
    `pdsid` int(11) NOT NULL auto_increment,
    `affiliateid` varchar(20) character set latin1 default NULL,
    `bpushno` longtext character set latin1,
    `psms` varchar(1) character set latin1 default NULL,
    `credits` varchar(5) character set latin1 default NULL,
    `mobileno` longtext character set latin1,
    `dlrid` longtext character set latin1,
    `dr` varchar(50) character set latin1 default NULL,
    `op` varchar(10) character set latin1 default NULL,
    `dtoken` varchar(200) character set latin1 default NULL,
    `sid` varchar(15) character set latin1 default NULL,
    `char` varchar(5) character set latin1 default NULL,
    `gid` varchar(20) character set latin1 default NULL,
    `msg` varchar(700) character set latin1 default NULL,
    `status` varchar(1) character set latin1 default NULL,
    `time` varchar(10) character set latin1 default NULL,
    `subdt` date default NULL,
    PRIMARY KEY  (`pdsid`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=2444466;

SELECT Query:

select  *
    from  gsm_smslog220717
    where  affiliateid ='hn137754388'
       && subdt = '2017-08-21'
       && status= 's' 

How can I improve speed of query? In one second many insert queries are also run on live.

Please help to create best index for this query.