choosing default kernel in grub

Hi!

trivial question, but couldn't find a good answer.

How do I set a specific kernel to be the default in grub to be booted?
In debian kernels are in the "advanced" section. So the easy way to set 
the default menu entry in grub is not working.

I updated the kernel 6.16.12+deb14-sparc64-smp but it doesn't work. 
Maybe the next update will or will not work.

I want to set it to my last known good working kernel version which his:
/boot/vmlinux-6.12.38+1-sparc64-smp


I would prefer not to uninstall the latest kernel or hold the kernel 
version, that way it is easy to test new kernels.

Riccardo