The forum picks up your name from when you first created an account. For some there is no name so it doesn't show in your posts.
To update your profile so your name shows with the posts, return to the home screen. In the upper right corner you will see a small bell and a V. Click on the V and and select profile. You will see three dots aligned vertically. Click on those dots and select edit. You can then fill in your name. Then scroll down and select Update to save the information.