Hello from Sweden 1969 Dart GT

Try adjusting the front band and see if second comes back.
My car didn't have second when I bought it, and it was just that the band was too loose to grab the drum for second, so it just skipped it and went straight for third.
Couldn't really tell there was anything wrong except it only had two gears.

The band could also be broken, which isn't all that bad to fix either.
It does have to come out for that though.