first put the software into the memory of the mobile phone or the memory card in the mobile phone, then move the cursor to that software and press the ok key to install it until it is finished.

Generally, users need to sign the software with certificates, and each mobile phone has a unique serial number. With the serial number, you can apply for a certificate only suitable for your mobile phone to sign the software you need. You need to go to Nokia to apply for the certificate yourself, but many mobile phone forums do this for free. They apply for a certain number of netizens together. When you apply for the certificate, you can sign your software with mobile phone (generally signature-free) signing software or computer signing software. To put it bluntly, a certificate is a passport with authority, which allows the software to be installed and used in your mobile phone.

Can't you find the software in a memory card folder you know?

you need to apply for your own certificate to sign and install the software with the wrong certificate.