How to create certificate request with "not after" parameter for Db2 SSL/TLS?

I have configured Db2 v11.5.7.0 on Linux/x64 to use SSL/TLS protocol and Db2 client can successfully connect to Db2 server using SSL/TLS. Now I would like to test certificate renewal. I need to create certificate request and then sign it with company CA with limitation of "not after" some date. I would like to set only few days certificate validity, so on my testing system I can test what happens when certificate expires. I am using gsk8capicmd_64 to create certificate request. I checked official documentation , but can't figure it out. When renewing certificate request how to specify that certificate is not valid after specific date?