Ans- First, Download the zip file from the below-given link.
2- Then, extract it using any extracting tool like WinRAR or 7zip.
3- Now, get the obb cache file and move it to the Android\\obb folder in your phone's internal memory/SDcard.
4- After that, rename the apk to the original name.
5- Now, you can install City Island 4 mod Apk on your phone.