Chabad.org — English translation + Rashi
Torah Temimah points to Menachos 58a.
E-Daf.com — Menachos 58a
HebrewBooks / Shas PDF
English: Might an individual vow and bring a first-offering as a free-will gift? The verse says “you shall offer a first-offering” — a communal [offering] I said to you, and not an individual.
Miyut of individual nedavah of reishit — only the community brings these forms.
Only the community brings the first-offering forms; an individual may not vow them as nedavah. The Torah’s plural “you shall offer” is read as addressing the community, not a private person who might wish to bring a free-will parallel.