Здесь проблем нет или https://www.db-fiddle.com/f/8UYVnC2xQsWuSC9VBZz6BN/0
DROP TRIGGER IF EXISTS T;
drop table if exists `manage_transaction`,manage_site_income_details;
create table manage_transaction(t_id int,txn_id int,fee int,about varchar(3),status varchar(15));
create table manage_site_income_details(id int,t_id int,txn_id int,txt varchar(20),fee int,dt datetime);
insert into manage_transaction values (1,1,10,'sub',null);
CREATE TRIGGER T
AFTER UPDATE ON `manage_transaction`
FOR EACH ROW
IF OLD.about LIKE 'SUB' AND NEW.status = 'Completed' THEN
INSERT INTO manage_site_income_details
VALUES(
NULL,
OLD.t_id,
OLD.txn_id,
'SUB_Fee',
OLD.fee,
NOW());
END IF;
update manage_transaction
set status = 'completed';
select * from manage_site_income_details;
+------+------+--------+---------+------+---------------------+
| id | t_id | txn_id | txt | fee | dt |
+------+------+--------+---------+------+---------------------+
| NULL | 1 | 1 | SUB_Fee | 10 | 2020-05-29 09:58:04 |
+------+------+--------+---------+------+---------------------+
1 row in set (0.001 sec)