What to do when AirPods won't connect to new case?

i lost my case but not my airpods. so i bought a new case n put my old airpods in it but it wont show on find my n it keeps sayinf "airpod mismatch" and “airpod setup incomplete” and it doesnt show the location of my airpod n case what do i do??

[Re-Titled by Moderator]

Original Title: lost my case but not airpod