Do you know which language area he is from?

If you are from a German-speaking area, then the more formal guten tag[gu:ten ta:k} is standard German. In Swiss German, you can say grüezi[grüezi:]!

You can say goodbye auf wiedersehen[aof vi:d?ze:en] or Swiss German Uf wiederluege[u:f vi:d?lu?g?]!

I can’t do anything else, because Swiss German is quite strange, and I only know a little bit about it. In fact, you can just speak standard German. For example, you can say: Gute Reise [gu:t? raiz?] when wishing others a safe journey.

Have a nice day is actually the most commonly used way of greeting among Germans. It is what I call used for meeting. This is the simplest way of saying it after removing some things. The complete saying is I wish you a nice day. , the phonetic notation may not be standard, I used the phonetic notation. r is the uvular sound, it doesn’t matter if you can’t pronounce it, just pronounce it in English as you want

Read it all according to my phonetic notation, t is t, watch phonetic symbols. . .