どうも (dōmo) means “thanks, thank you”

More examples

手伝ってくれた友だちに、どうもと言います。te tsuda tte ku re ta tomo da chi ni dō mo to i i ma su

I say "Thank you" to my friend who helped me.

どうも、手伝ってくださってありがとうございます。dō mo te tsuda tte ku da sa tte a ri ga tō go za i ma su

Thank you very much for helping me.

Signals gratitude in a short, relaxed way without the formality of a complete polite phrase.

ありがとうarigatō: An interjection used to express thanks in everyday speech.

何かをしてくれた相手への感謝を簡潔に表す言葉。nan ka o shi te ku re ta ai te e no kan sha o kan ketsu ni arawa su koto ba

As a word for thanks, どうも (dōmo) comes from the longer expression どうもありがとう (dōmo arigatō), whose first part was later used on its own.

When a small favor is completed, どうも (dōmo) provides a natural casual thanks, whereas ありがとうございます (arigatō gozaimasu) suits more formal situations.