Adding Dotted Minims

I would like to transcribe a piece of music that is in three four time, and
part of it needs dotted minims with two extra crotchets in the same bar. The
dotted minim needs to be held for the entire length of the bar and the
crotchets are played at the same time. The program changes the dotted minim
into a crotchet, which is not what I want and I don't know how to keep both
the dotted minim and the other crotchets. How can I do this without adding in
another keyboard staff?