How to do a recursive sum of children in mysql?
With your example, you can run
CREATE PROCEDURE procedure_name()
BEGIN
        DECLARE finished INTEGER DEFAULT 0;
        DECLARE _accoujntno INTEGER DEFAULT 0;
        DECLARE _uacn varchar(191) DEFAULT &quot;&quot;;
    DEClARE curaccount 
        CURSOR FOR 
            Select account_no ,user_account_number FROM TBL1 WHERE length(user_account_number)-length(replace(user_account_number,'-',''))+1  = 2 order by user_account_number;

    -- declare NOT FOUND handler
    DECLARE CONTINUE HANDLER 
        FOR NOT FOUND SET finished = 1;
        
        CREATE TEMPORARY TABLE credits(
        user_account_number VARCHAR(191),
        `Debit_Before_Period` DECIMAL(20,2),
         `Credit_Before_Period` DECIMAL(20,2),
         `Debit_In_Period` DECIMAL(20,2),
         `Credit_In_Period` DECIMAL(20,2)
        );
        
        OPEN curaccount;

    getaccount: LOOP
        FETCH curaccount INTO _accoujntno,_uacn;
        IF finished = 1 THEN 
            LEAVE getaccount;
        END IF;
                INSERT INTO credits SELECT _uacn ,SUM(`Debit Before Period`),SUM(`Credit Before Period`) ,SUM(`Debit In Period`) ,SUM(`Credit In Period`)  
                FROM TBL1 
                WHERE LEFT(user_account_number,7) = _uacn AND account_no &lt;&gt; _accoujntno;
    END LOOP getaccount;
    CLOSE curaccount;

   SELECT * FROM credits;
END 

The resulting temporary table credits you can use to run  further analysis
simply add the procedure and CALL procedure_name()
In a query tab in phmyadmin wor mysql Workbench you need to add DELIMITER to the procedure, but that doesn't work in dbfiddle
example
It is like in the comment
CREATE PROCEDURE procedure_name()
BEGIN
        DECLARE finished INTEGER DEFAULT 0;
        DECLARE _accoujntno INTEGER DEFAULT 0;
        DECLARE _uacn varchar(191) DEFAULT &quot;&quot;;
    DEClARE curaccount 
        CURSOR FOR 
            Select account_no ,user_account_number FROM TBL1 WHERE length(user_account_number)-length(replace(user_account_number,'-',''))+1  = 1 order by user_account_number;

    -- declare NOT FOUND handler
    DECLARE CONTINUE HANDLER 
        FOR NOT FOUND SET finished = 1;
        
        CREATE TEMPORARY TABLE credits(
        user_account_number VARCHAR(191),
        `Debit_Before_Period` DECIMAL(20,2),
         `Credit_Before_Period` DECIMAL(20,2),
         `Debit_In_Period` DECIMAL(20,2),
         `Credit_In_Period` DECIMAL(20,2)
        );
        
        OPEN curaccount;

    getaccount: LOOP
        FETCH curaccount INTO _accoujntno,_uacn;
        IF finished = 1 THEN 
            LEAVE getaccount;
        END IF;
                INSERT INTO credits SELECT _uacn ,SUM(`Debit Before Period`),SUM(`Credit Before Period`) ,SUM(`Debit In Period`) ,SUM(`Credit In Period`)  
                FROM TBL1 
                WHERE LEFT(user_account_number,3) = _uacn;
    END LOOP getaccount;
    CLOSE curaccount;

   SELECT * FROM credits;
END 

new example