The groups you see in Ommnio are all the ones that the organization considers to be of interest to you.
However, maybe comparing your Ommnio app with that of another colleague, you have seen that there is a group that could be of interest to you. If so, you should contact the administrator of your organization in Ommnio (people from Human Resources, Communication, or General Management), since they are the ones who manage which users have access to each group. Only they can add and remove participating users in each group.
If they consider it appropriate, they can add you to a group from the web version of Ommnio. Pass them this article if they don't know how to do it 👉 How to add or remove a user from a group