This is another of the concertos attributed to Mozart or his circle, likely dating from his earlier period. It embodies the clear, elegant style of the Classical era, with balanced phrasing and tuneful melodies suitable for the bassoon.
Focus on achieving a pure tone and graceful phrasing, especially in the slow movement.
Bassoon Concerto in B-flat major is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
Bassoon Concerto in B-flat major is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.