You may need to get everything assembled and have another help you until it gets easier. Here are some threads about tube feeding and a video:
https://www.backyardchickens.com/threads/go-team-tube-feeding-updated-12-29-2019.805728/
https://www.backyardchickens.com/threads/go-team-tube-feeding-updated-12-29-2019.805728/