MySQL Stored Procedure IF multiple statement

Hi,

this is my stored procedure on database MySql version 8.0.17

CREATE DEFINER=`root`@`%`PROCEDURE`SP`(IN tun CHAR(100), tmonth CHAR(100))BEGINIFRIGHT(tun,2) = '00'THENSET @s = CONCAT('SELECT * FROM `t_ri` WHERE LEFT (t.un, 2) = LEFT(\'',tun,'\',2);');
ELSESET @s = CONCAT('SELECT * FROM `t_ri` WHERE t.un = \'',tun,'\';');	ENDIF;PREPARE stmt FROM @s;EXECUTE stmt;DEALLOCATEPREPARE stmt;SELECT @s;END

I need insert a new IF condition in stored procedure when the value of variable tmonth is not null.

If variable tmonth is not null and RIGHT(tun,2) = '00' the query it should be

SET @s = CONCAT('SELECT * FROM `t_ri` WHERE LEFT (t.un, 2) = LEFT(\'',tun,'\',2) AND tmonth = \'',tmonth,'\';');

else

SET @s = CONCAT('SELECT * FROM `t_ri` WHERE t.un = \'',tun,'\' AND tmonth = \'',tmonth,'\';');

I have tried multiple conditions but none have ever worked… can you help me?