open up

to start to talk more about yourself and your feelings:
I've never opened up to anyone like I do to you.
(Cambridge Advanced Learner's Dictionary & Thesaurus からの open up の定義 © Cambridge University Press)

アメリカ英語辞典
(used as an exclamation) let me in; open the door:
"Open up!" Sam shouted, banging on the door.

to talk about your personal thoughts or feelings:
I felt I couldn’t open up to anybody.
(Cambridge Academic Content Dictionary からの open up の定義 © Cambridge University Press)

ビジネス英語
if a new business, office, shop, etc. opens up, or someone opens it up, it starts doing business:
Several branches of the bank have recently opened up across China.
Many people have opened up shops on the online auction site to sell their things.

to start business at a particular time and be available to deal with customers:
We open up at 7am daily.

to make conditions easier for foreign companies to do business in a country:
These measures are designed to open up the market to greater competition.
The country has enjoyed steady growth since it began opening up its economy.

to create new opportunities:
open up opportunities/possibilities The internet has opened up new opportunities for cost-effective brand building.

if a job opens up, it becomes available:
Another vacancy has opened up on the Board.
(Cambridge ビジネス英語辞典 からの open up の定義 © Cambridge University Press)

- Cambridge Dictionary