One of our certificate is about to expire and by using keytool explorer i selected the .jks file and in that many certificates are there and one is expiring. To renew that certificate i have exported the certificate by using the keystore explorer and got a .cer file. when i shared the .cer file to the client he asked to send the csr file.
You should be selecting the Generate CSR
option for that key pair. This will generate the CSR that you need to send.