You seem to be asking about these two verses regarding who talked to Mary:
إذ قالت الملائكة يا مريم إن الله يبشرك بكلمة منه اسمه المسيح عيسى ابن مريم
When the angels said, "O Mary, indeed Allah gives you good tidings of a word from Him, whose name will be the Messiah, Jesus, the son of Mary ..."
— Quran 3:45
فأرسلنا إليها روحنا فتمثل لها بشرا سويا ... قال إنما أنا رسول ربك لأهب لك غلاما زكيا
Then We sent to her Our Spirit, and he represented himself to her as a well-proportioned man ... He said, "I am only the messenger of your Lord to give you [news of] a pure boy."
— Quran 19:17-19
The spirit ( روح ) mentioned in the latter verse is Gabriel, who is among the angels and is their chief. The word angels ( الملائكة ) in the earlier verses also refers to him alone according to many exegetes.
That is because in Arabic language, a plural or genus can be used to refer to a single individual. There are many examples of this in the Quran, a few are as follows:
Plurals are used throughout the Quran for Allah, while He is one.
إنا نحن نزلنا الذكر وإنا له لحافظون
Indeed, it is We who sent down the Qur'an and indeed, We will be its guardians
— Quran 15:9
Messengers ( رسل ) is used, while what is meant is one prophet:
يا أيها الرسل كلوا من الطيبات واعملوا صالحا
O messengers {i.e. Muhammad or Jesus}, eat from the good foods and work righteousness.
— Quran 23:51
وقوم نوح لما كذبوا الرسل
And the people of Noah - when they denied the messengers {i.e. Noah}
— Quran 25:37
People ( الناس ) is used, while what is meant is one individual:
الذين قال لهم الناس إن الناس قد جمعوا لكم فاخشوهم
Those to whom people {i.e. Nuaym ibn Masud} said, "Indeed, the people have gathered against you, so fear them."
— Quran 3:173
أم يحسدون الناس على ما آتاهم الله من فضله فقد آتينا آل إبراهيم الكتاب والحكمة
Or do they envy people {i.e. Muhammad} for what Allah has given them of His bounty? But we had already given the family of Abraham the Scripture and wisdom
— Quran 4:54
Mosques ( مساجد ) is used, while what is meant is one specific mosque:
ما كان للمشركين أن يعمروا مساجد
It is not for the polytheists to maintain the mosques { i.e. Masjid al-Haram}
— Quran 9:17
Another possible explanation is that the news was given twice to Mary, once by a group of angels and once by Gabriel alone - so the two verses mention two separate events.
Reference:
وجائز في العربية أن يخبر عن الواحد بلفظ الجمع
It is valid in Arabic to give news of one person with a plural word
— Tafsir al-Qurtubi