You have to reinstall it on your mobile phone. Topics usually need to be signed. Those that have not been cracked shall not be installed and used. Just like installing QQ on a mobile phone, downloading it to a mobile phone needs to be installed on the mobile phone once.

If it is cracked, you can follow the following steps: find the downloaded theme (actually an installation package) in the mobile phone folder, and remember which folder you are in when downloading.

Then click Install and wait for the installation to succeed.

Then open the phone settings-personal mode-theme mode-standard-and the theme option you just installed will appear. Just click twice.