Greetings, @Jindowin
When you enter a Pokecenter you can interact with the Computer, which will open your PC. You should be able to see the other pokemon you have caught previously in the first Box (Number 1) of your PC.
Could you check if you are able to see the other pokemon you have caught and access them? To place them in your team, you only need to manually drag them from your Box to your Team.