While building a new kernel i forgot to change the name of CONFIG_LOCALVERSION in the .config file as a result my current kernel got replaced by the one I was building. My original kernel still exists as Pop_OS-oldkern.conf, and I can still boot into it once booting into the new kernel fails. 

Is there any way to reverse this?

I know I could just reinstall my OS again but I have some deadlines coming up and can't afford to lose time in setting things up on my system :(

Regards, 

palash