Here is a method to do it. I'm sure your situation is slightly different but maybe something similar to this might work for you:
create table test_t(
datef char(10),
timef char(8),
datetimef datetime)
insert into test_t (datef, timef) values ('01/01/1990','09:15 PM')
insert into test_t (datef, timef) values ('07/21/2001','03:13 AM')
insert into test_t (datef, timef) values ('06/03/1967','10:49 PM')
update test_t
set datetimef = cast(datef + ' ' + timef as datetime)
select * from test_t
dropt test_t
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