How do I find similar similar channels?

Hi. There is a channel and I want to find other channels that are as relevant to this channel as possible. How can I do this? Are there any services for this? Thank you in advance

i don't know if there is a service for this but you can do it manually:
first, find the keywords for the channel (Top Keywords if you are using VidIQ.. send me a pm if you couldn't have them)
then, do a Youtube search.. the top results usually are the channels you need to follow.