Or to put it another way, you need to keep a database/table/JSON flat file/config file, something somewhere that keeps a list of the channels that your bot should be in that persists between restarts of your bot.
To answer this question directly, no, there is no API that lets you go get “channels I am a mod in” in order to go and join those channels.
Nightbot has a database table that lists all the channels, commands, users, it’s interest in, so at Restart, it just checks the table and goes from there, (it’s way more complicated, but what I wrote is valid for smaller bots)