I just wrote this for your reference. If you have any questions, you can ask. There's still plenty of time

day1 train arrives in Xiamen, so book the accommodation for that night in advance. I suggest living in Zeng Cuo An Village. There are many inns there, and the environment is very good. The Mark Inn where I lived at that time was very comfortable. Eat casually around in the evening to save energy for the next day.

Get up in the morning on Day 2, or eat casually around. There is a famous snack bar there, and the taste is ok. There is a lot of breakfast around, and the inn should also have breakfast. Then rent a bike and ride along the island road. The scenery is very good! Come back at noon to have a simple rest, eat something, take a bus tour to Xiamen University in the afternoon, and experience it in the canteen of Xiamen University in the evening!

on day 3, I went to the city center in the morning, took the BRT in Xiamen, visited Hulishan Fort and other places, tasted the delicious food in the city center, went shopping and so on. In the evening, go to a popular food stall in the city center to eat seafood, which is delicious and cost-effective!

on day 4, I suggest that you leave your luggage in the inn, go to Longyan for a day, and just take the train. It is best to get off at Yongding directly, go back to Xiamen from Tulou in the morning on day5, book an inn in advance after picking up your luggage, and stay in Gulangyu.

On day 6, continue sightseeing in Gulangyu during the day, check out in the afternoon and return to the city, thus ending the pleasant trip to Xiamen.

ps I wrote it from the perspective of a tourist, so you can ask questions. hope this helps