先日はどうもありがとう。

the other day; a few days ago

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

thanks; much (thanks); very (sorry); quite (regret); quite; really; mostly; somehow; in spite of oneself; no matter how hard one may try (one is unable to) (with negative verb); no matter how hard one may try not to (one ends up doing) (with positive verb, esp. -shimau); greetings; hello; goodbye

Thank you; Thanks