Ok, so here was my process:
keytool -list -v -keystore permanent.jks – got me the alias.
keytool -export -alias alias_name -file certificate_name -keystore permanent.jks – got me the certificate to import.
Then I could import it with the keytool:
keytool -import -alias alias_name -file certificate_name -keystore keystore location
As @Christian Bongiorno says the alias can’t already exist in your keystore.