How do you say "I'm back/here" in Korean?
For example if I were texting my Korean language partner and I had to go to eat, do chores, go out to the shop, or just be away from the phone in general, what would I say when I returned.

Me: I have to go now to eat my lunch. I'll be back soon!
Friend: Okay, bye!
Me (A while later): I'm back

Thank youuuu

Question

How do you say "I'm back/here" in Korean?
For example if I were texting my Korean language partner and I had to go to eat, do chores, go out to the shop, or just be away from the phone in general, what would I say when I returned.

Me: I have to go now to eat my lunch. I'll be back soon!
Friend: Okay, bye!
Me (A while later): I'm back

Thank youuuu

Answer

It is simple. You don't need to say something special. 
I think You can say hello again in the context. 
" 안녕, 안녕하세요, Hi/Hello" 
"뭐하세요? 뭐해요? 잘지내요?, How are you? "

"저 돌아왔어요, 나 돌아 왔어" is translated Literally. so,this sentence is also correct.

and I think that this sentence is possible. "I'm ready to say again , 저는 다시 당신과 대화할 준비가 되었습니다."

Answer

It is simple. You don't need to say something special.  
I think You can say hello again in the context.  
" 안녕, 안녕하세요, Hi/Hello" 
"뭐하세요? 뭐해요? 잘지내요?,  How are you? "

"저 돌아왔어요, 나 돌아 왔어" is translated Literally. so,this sentence is also correct.

and I think that this sentence is possible.  "I'm ready to say again ,  저는 다시 당신과 대화할 준비가 되었습니다."

Answer

저 돌아 왔어요!