What does the cryptic crossword clue "Unwind the flexes with plug in (7,2)" mean?

The definition is "Unwind". The wordplay uses an anagram. anagram of THE + PLUG + IN = LIGHTENUP; definition: "Unwind" The answer is LIGHTENUP.

Unwind the flexes with plug in (7,2)

Independent Cryptic #10867 | 1 Down | 2021-08-11 flower