tsql update (help me)

i have 3 tables

tbl_indicator
grp_nbr   sect_nbr   indicat
1             100          p
2             101          s


tbl_group
grp_id    grp_nbr    sect_nbr     indicat
333         1              100           a
555         1              100           p
444         2              101           s
222         2              101           y

here (in tbl_group) grp_id is P.K

tbl_order
order_id       grp_id
5000              333
5001              555
5002              555
5003              555
5004              444
5005              444
5006              222
here (in tbl_order) grp_id is F.K to grp_id in tbl_group


now the thing is that in table tbl_indiactor for one set of grp_nbr and sect_nbr there is an indicat, for the same set of grp_nbr and sect_nbr there is a correct indicat(333,1, 100, p) and a junk indicat(555, 1, 100, a) in table tbl_group.
but both these grp_id s(333, 555) are present in table tbl_orders
now i need to update tbl_order table in such a way that the junk grp_id s should replace with correct grp_id s

the output should like

tbl_orders
order_id       grp_id
5000             555
5001              555
5002              555
5003              555
5004              444
5005              444
5006             444

can some one help me please.....

My first step is to find the values needed in a select.  I then use that select as the basis for the update statement. 

I think this is what you want.

declare @t_indicator table (grp_nbr smallint, sect_nbr smallint, indicat char(1));
declare @t_group table (grp_id smallint, grp_nbr smallint, sect_nbr smallint, indicat char(1));
declare @t_order table (order_id int, grp_id smallint);

insert into @t_indicator (grp_nbr,sect_nbr,indicat) values (1,100,'p') ,(2,101,'s');

insert into @t_group (grp_id,grp_nbr,sect_nbr,indicat) values
(333,1,100,'a'),(555,1,100,'p'),(444,2,101,'s'),(222,2,101,'y');

insert into @t_order(order_id,grp_id) values
(5000,333),(5001,555) ,(5002,555), (5003,555),(5004,444),(5005,444),(5006,222);


update o set o.grp_id = qGood.grp_id
from @t_order o
join @t_group g on g.grp_id = o.grp_id
join @t_indicator i on i.grp_nbr = g.grp_nbr
join (
    select g.grp_id,g.grp_nbr,g.sect_nbr,g.indicat
    from @t_group g
    join @t_indicator i on i.grp_nbr = g.grp_nbr
    where g.indicat = i.indicat
) qGood on qGood.grp_nbr = g.grp_nbr
       and qGood.sect_nbr = i.sect_nbr
       and qGood.indicat = i.indicat
where g.indicat <> i.indicat

---------
select * from @t_order