Your Artist Ids on Spotify and Apple music are the string of numbers and letters at the end of your profile URL:
https://open.spotify.com/artist/0HtD8SjUM1lm2jP7jAeXu2
https://music.apple.com/fi/artist/warmland/376150162
Go to your artist profile on Spotify or Apple Music and click on the ••• icon and click copy link.
You must add your id numbers when uploading your music for global distribution if you already have an artist page on Spotify or Apple Music. If you don't already have an Artist number please leave blank and one will be provided for you.