It’s kind of tedious, but you can do it with a tool like the DMT Diafold Serrated Knife Sharpener. On most serrated knives, you will also want to lightly sharped/deburr the other face at an extremely shallow angle using a whetstone that either you don’t care about too much or that is extremely resistant to scratching (e.g. a DMT-style flat stone). If you do that part on something like a traditional Japanese stone, you will make a mess.