Can't generate the initrd.gz image. Now what?

I had to reinstall Slackware and was trying to generate the initrd.gz image. I get this:
root@darkstar:/boot# /usr/share/mkinitrd/mkinitrd_command_generator.sh
Modules for kernel 5.15.19 aren't installed.
The new kernel is 5.15.139. What do I do?

Thanks