How do I find out the second number for my control number on my W2? It has 7, but when reviewing it said there's supposed to be 2 numbers; what do I do?

What?  Where?  The W2 Control number?   W2 box d Control number is not needed.  See

https://ttlc.intuit.com/community/forms/help/i-have-no-box-d-or-control-number-on-my-w-2/00/26469

The control number in box d is not required by the IRS - it is used by your employer.  As a result, if it causing you trouble, just delete it.  If it is not causing you trouble, then leave it in - it won't matter.