Please handle the rest as you see fit.
Please make the arrangements for the details as you think best.
Usually written in kana; the kanji form 良しなに exists but is less common.
Kanji form; learners may encounter it, but kana is preferred.
Derived from the classical adjective よし (good) + なに (adverbial particle). The exact historical development is uncertain, but it has been used since at least the Edo period to mean 'in a good way' or 'as you think best'.