Not sure about that 2nd lens. Possibly a 2nd eyepiece? Is there any writing on it? Perhaps a 10mm or 9mm eyepiece for higher power?
Just try experimenting with it. Do the list of contents state there should be a second eyepiece?
These things usually come with 2.
Again, glad I could help. A Merry Xmas to you and your family.
Enjoy the scope and feel free to keep asking questions and share your experiences with all of us here at IIS
