Update Lowest ID Only
you could try something like:

update h
set sal = t.sal
from @Helper h
join (
    select h.empname, h.saleid, h1.sal, row_number() over(partition by  h.empname order by h.saleId ) as n
    from @Helper h
    join @Helper1 h1 on h.empname = h1.empname
    ) t on h.empname = t.empname and h.saleid = t.saleid
where n = 1


(assuming the primary key of @Helper in on empname + saleid)