Last character in column shift to next column
Here is a trivial way using left, right, and stuff.

declare @table table (column1 varchar(16), column2 varchar(16))

insert into @table
values
('abcdef','ghijkl')

update @table
set 
    column1 = left(column1,len(column1) - 1)
    ,column2 = stuff(column2,1,0,right(column1,1))

select * from @table


If you have trailing spaces, you'll need to use RTRIM accordingly.

column2 = stuff(column2,1,0,right(rtrim(column1),1))


After fixing your sample data to add commas in your DDL, and removing the extra column from the insert, you can still use the method above with a small tweak:

declare @dda table
(
    comp_acct_num varchar(17)
    ,internet_code char(3)
    ,type_code char(1)
    ,cr_rate_code char(1)
)

INSERT INTO @dda (  comp_acct_num,
                    internet_code,
                    type_code,
                    cr_rate_code) 
VALUES 
 ('00000000000000000','111','7','')
,('00000365874001000','111','7','')
,('00000000000001000','211','7','')
,('00003101118001000','211','7','')

update @dda
set 
    comp_acct_num = left(comp_acct_num,len(comp_acct_num) - 1)
    ,internet_code = left(stuff(internet_code,1,0,right(comp_acct_num,1)),3)

select * from @dda