Departure: Chengdu → Kuala Lumpur → Kota Kinabalu, return trip: Kota Kinabalu → Kuala Lumpur → Chengdu (we will stop in Kuala Lumpur for one day on the way). How should I apply for a visa?

First, Kuala Lumpur and Kota Kinabalu are both in Malaysia, so you only need to apply for a Malaysian visa. What you need to apply for is a tourist visa, a single-entry visa.

Second, in Chengdu, travel agencies and agencies specializing in visa processing can apply for Malaysian visas on their behalf. You can check on Taobao and find a visa agency with an office in Chengdu, so that you can go to its office in person to apply without having to mail your passport. If there is a problem during the application process, it is also a problem with the agency, and you can go to them. This is how I applied for a visa to go abroad. It was applied at an agency specializing in visa processing near Hongxing Road Pedestrian Street. This is mainly for convenience and peace of mind. The visa for Malaysia is about 350 yuan.