How to solve the problems of lag and regional restrictions when using domestic software while studying in South Korea?

Upon arriving in South Korea, I discovered that a bunch of apps on my phone had suddenly stopped working. WeChat worked, but the videos in Moments were endlessly loading; Douyin worked, but the trending content was different—the domestic and international versions are essentially not the same product; and some content on Bilibili wouldn't open, displaying the message "Current region…".