Please tell me the Islamic ruling regarding cutting/trimming of women's hair in beauty parlors.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

If this trimming or cutting is not done as an imitation of men or disbelieving women, then it is lawful because the wives of the Prophet (Sallallahu Alaihi wa Sallam) used to cut some of their hair as reported by Muslim from Abi Salamah Ibn Abderrahman Ibn Awf . They used to do this to make the hair easier to handle. al-Nawawi said, 'While explaining this Hadith' . "This is an evidence that it is lawful for women to cut some of their hair" .
But if the woman intends to imitate men or disbelieving women then it is highly prohibited. al-Bukhari reported that the Prophet (Sallallahu Alaihi wa Sallam) "cursed the men who imitate women and the women who imitate men" .
And there are several Hadith warning against imitating non-believers and even ordering Muslims to do the opposite of what the non-believers do.
However, some scholars prohibited women to cut their hair except for necessity such as treating some wounds which cannot be treated otherwise. Then what is cut should not exceed the minimum necessary.
There is no difference in what we mentioned between cutting one's hair at home or having it cut in beauty parlors.
As for the rule of opening beauty saloon or parlors, it is lawful provided it is free from anything that conflicts with Sharia like exposing Awrah or helping prostitutes and dissolute women in their vice and the like.
Allah knows best.