I am a chest breather and find that when I try to use the abdomen as the primary object I become agitated because I have to force myself to use abdominal breathing in order to feel any kind of motion there.
Indeed, it is important not to force the breathing - not to slow it down, nor to speed it up... and not to seek for anything to see in particular. That creates tension and agitation.
You can start observing the breath at the chest or the sitting and touching points. They are obvious objets, appearing clearly in the mind.
Then, slowly, you can start to deepen your breaths. Indeed, in the beginning, for those who are not yet used to breath from the abdomen, it is helpful to train to make complete and full breaths, as Sayadaw U Pannathami (Panditarama Sydney Sayadaw) advises. It means that we try to breath in fully and completely so that the air goes down to the abdomen ( and thus, bringing more oxygen to the body). It is very relaxing to breath in such a way.
Then you just need to direct your attention to the abdomen aera to see what is happening there.
May you enjoy your practice.