Generally speaking, each fund company can log in with its own ID number to inquire about the fund holdings. Some companies may ask you to enter your personal fund account number. In this case, you can go to the institutions that buy funds (such as banks and brokers).

The same identity document has only one account number in a fund company.

If it is a newly purchased fund, I'm afraid I can't find the fund account number before the fund company confirms it. When the fundraising is over and the fund contract comes into effect, I can find the account number in the same way.