Cool your beans? Go and see him about that? Correct?
I am playing a online game, and one of NPCs (Non-player character in world of game) said me :
"You tend to get stressed out. You ought to chew on some great dishes every now and again to cool your beans."
I searched my dictionary on "bean".
Bean can refer "head" as well. right? But this NPC is saying "beans" as the plural form, in spite of one head my character has.

You think it is just typo? Or natural sentence? Please explain me.

Second question.
I recieve a task from a NPC saying "Go and see him about that."
You feel this line is natural and correct?
"ask about that" or "speak to him about that" make sense for me though.
But I have never run into like this phrase "see somebody about something", ins't there?
Please tell me about your opinion.

I know it might be silly to seek perfectly correct English grammar from NPCs in games, but I believe that this makes me more improve my English skills.

Question

Cool your beans? Go and see him about that? Correct?
I am playing a online game, and one of NPCs (Non-player character in world of game) said me : 
"You tend to get stressed out. You ought to chew on some great dishes every now and again to cool your beans."
I searched my dictionary on "bean".
Bean can refer "head" as well. right? But this NPC is saying "beans" as the plural form, in spite of one head my character has.

You think it is just typo? Or natural sentence? Please explain me.

Second question.
I recieve a task from a NPC saying "Go and see him about that."
You feel this line is natural and correct?
"ask about that" or "speak to him about that" make sense for me though.
But I have never run into like this phrase "see somebody about something", ins't there?
Please tell me about your opinion.

I know it might be silly to seek perfectly correct English grammar from NPCs in games, but I believe that this makes me more improve my English skills.

Answer

I'm not familiar with "cool your beans." I can't say I've ever heard somebody say that phrase before, but I have definitely heard "go and see him about that." That is very normal and natural in English. When we use "see" in that sense, we mean it as "talk to" or "ask about." Similar to how we would say, "You should go and see a doctor about your injury." We're implying that you could go visit the doctor and ask him for his medical opinion.

Answer

"Cool your beans" is just a slang phrase. It means "calm down." The person is giving you advice on how to relax your nerves.

I think Alicia's explanation of "go and see him about that" is good, so I don't need to answer that part of your question.

Answer

I also wonder if "cool your beans" means to take some time out and let your "hot meal" cool down.  I don't think "beans" automatically means "heads". You can also say "nut" for head, but if you say "nuts"... :)

Either way, it's not a typo. You can find a number of other examples online.

By the way, "please explain this sentence" would mean "this sentence" is a mystery to you. Think about how native speakers understand "please explain me". :)

Alicia's explained the other phrase perfectly fine. Yes, it's common and natural as well.