The 2nd person command for verbs ending in -ire and -ere is the same as the normal 2nd person present conjugation (in this case, "senti"). It's only the -are verbs that are different (for example, the 2nd person imperative of "aiutare" is "(tu) aiuta" while the 3rd person command is "(lei) aiuti").
A source you can check out: https://www.thoughtco.com/italian-verb-conjugations-aiutare-4083615
This is so bad. They should have left this phrase out completely given the many possible translations to English. "Jumper" may be common in the UK (see Belle and Sebastian's "Dress Up in You"), but it is never used in the US. "Woolen" is also not common in the US. "Sweater of wool" was rejected. "Jersey" is something one only wears in an organized sport or perhaps on a road bike ride. Or, on the east coast, as a common abbreviation of "New Jersey" (see "Frankie's Gun" by The Felice Brothers.) Go figure. Idiomatically.