If this fashion company contributes to immorality (such as people immodestly displaying the clothes) and investing in this company directly supports this, then it would be Haram. However, if your investment in this company supports the other activities of this company and doesn’t directly support the immodest display of clothes, then it’s fine.

You may find several rulings here on work and investment:

https://www.sistani.org/english/book/46/

Also here:

https://www.al-islam.org/a-code-of-practice-for-muslims-in-the-west-ayatullah-sistani/work-investment

You may sell your shares and withdraw from the investment if it is deemed that it is haram.