Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

In answering your question, I cannot do any better than quoting from one of my earlier answers to a similar question:

“If you start fasting one day earlier in one country and end up in another country for ‘eid al-fitr, where they start a day or two late, then you do not fast, but simply observe ‘Eid with them. You are not allowed to eat and drink in public in order to observe the sanctity of Ramadhan.

Having said this, I must add, the above answer only applies if you have already completed 30 days of fasting. Otherwise, you should fast with them.

The above ruling is based on the tradition reported from the Prophet (peace be upon him): “Fast with the people; break your fast with the people, and celebrate sacrifice with the people.” (Reported by Tirmidhi on the authority of Abu Hurayrah). Commenting on this tradition, Imam Ibn Taymiyyah states: “Based on this, a person traveling from one country where they started the fast earlier to another country where they started late, should follow the latter in the ‘Eid celebration. For such matters are not left to individuals to decide on their own; rather one should do so with the community.

This is also in conformity with the general principles of Islam, which counsel Muslims to foster a sense of unity and brotherhood. The Prophet said, “Hold firmly to the community; for a wolf preys easily on the stray sheep.” (Quoted by Nawawi in al-Majmu’)

Almighty Allah knows best.