How do You Install a Private Key on an iPhone Distribution Certificate?

When I try to validate my app after archiving, at the end it would say that I need a private key for a certificate.

I am a beginner with swift and I'm trying to complete my first app, and I tried to check out the settings of the certificate, but I couldn't find any way to install the private key for the certain type of certificate.

I expected to get the private key file, but I didn't.

Thanks, I_Like_Basketball

Solution

This may sound silly, but all what I had to do was restart the computer and it worked.