【Step 1】 First, you need an 'ES File Explorer', as shown in the image
【Step 2】 Open ES File Explorer, find the data package you downloaded that has garbled files, and open it (because I don't have a problematic data package on my phone, I just use a random one instead)
【Step 3】 After entering, you will find that everything inside is garbled files, and decompressing them is useless.
So at this point, click the 'Encoding' option at the bottom left
After entering, it will look like this
【Step 4】 Click the one circled in red, 'xxxx(GBK)', then hit OK, and it's done
Hope this helps everyone. This was discovered by Wu Yizhong.
