declare @test table (Col1 varchar(50))
insert into @test
select '[abcdef] Client' UNION ALL
select '[gdhdnuidd] 1st Party SW' UNION ALL
select 'testbusiness' 

select case when charindex(']', Col1) > 0 then substring(Col1, Charindex(']', Col1)+2, 50)
       else Col1 end
  from @test

declare @table table(
string varchar(50)
)
insert @table (string)
select '[gdhdnuidd] 1st Party SW'
union all select '[abcdef] Client'
union all select 'testbusiness'

select 
        case 
                when charindex(']',string) > 0 then right (string, (len(string)- charindex(']',string)))
                else string 
        end finalstring
from @table