There is no R. The two words "colonel" and "kernel" are completely different words, but they are pronounced exactly the same way! A "colonel" is a military rank. A "kernel" is a seed inside of a husk or nut.

Interesting reason behind why we actually pronounce an R but don't use one in spelling: https://www.smithsonianmag.com/smithsonian-institution/why-colonel-pronounced-r-and-more-questions-our-readers-180953036/

This is a very interesting word, one you need to simply memorize.