Download the certificate and find it on the application website. You can usually find it by entering the serial number. If you want to download the signature tool, there will be a prompt where the certificate is downloaded. Now, open the signing tool, click the certificate and right-click the -import certificate. That's all. It should be noted that it seems that only one certificate can be installed on a computer. After the installation is completed, right-click the software you downloaded that needs to be signed, and you will be prompted to sign the software. You can use it as long as you sign it. Finally, copy the signed software to the mobile phone, find and install it. That's enough.