what is 把那 means?

把那+V，把control（an action）

那 that things

V-the action

eg：把那吃了，eat that，把那拿来，take that here

you could simply understand 你得先把面吃完。 那means specifically the noodles you left earlier.

现在你把这个问题搞懂了吗？

Well, 把那 is not a phrase, so we should try to understand these two characters seperately.

“那”  means “that; the"   for example, 那个女孩  that/the girl    

“把” is more than just a character, it actually forms a very important sentence structure in Chinese.

Grammatically it is called “把”字句, which is used to express to apply an action on a certain object. The difficult part is that there are a few “把” sentence structures and one may find it impossible to learn all of them at once. 

So I'll just explain one of the structures which means to move something and put it somewhere.

Take a look at a couple of example sentences and you'll have a better understanding.

1. 把书放在书包里。Put the book in the schoolbag.     Structure: 把 +object+ Verb +在 + place

2. 把瓶子扔到垃圾桶里。 Throw the bottle into the trash can.   Structure:  把+object + Verb + 到 + place

I hope this can be of a little help.

Back to the sentence you mentioned in your question, 

把那碗面吃完。    Finish  that bowl of noodles.    Literal translation: 把that bowl of noodles + eat + finish

I'll give you a few more example sentences like this one to help you understand the structure.

把作业写完。  Finish the homework.    Literal translation: 把 homework + do + finish

把桌子擦干净。Wipe the table clean.      Literal translation: 把 table + wipe + clean
 

那means that，used before a noun. 把before a thing, means a thing need to be what

this is a "把" sentence. "那面" refer to "that bowl of noodles", and not "this bowl of noodles". it has nothing to do with "把". briefly form : 你把(那(碗))面吃完。