Firstly, the $125 claim is pretty much false advertising. They only have $31M set aside for this 'alternative compensation', while the breach impacted 147 million people. If just 1% of people affected request the alternative compensation the actual amount per person would be $21. I imagine the response has been significantly higher, if so the payout will be significantly lower.
The overwhelming response is why they are now pushing to get people to switch to credit monitoring. Personally, I bank with CapitalOne and they use CreditWise which says: "Monitor your credit. For free. For everyone." Whether or not their services are as pro-active or robust as what is being offered in the settlement doesn't seem material to me, it is a form of credit monitoring that I already have.
That said, while I could indicate that I have credit monitoring, at this point I'm thinking that the cash payout will be so small that it might be a better value to get the credit monitoring they offer since it does include some identity theft insurance.
I've not done too much research on the settlement, but the FTC site has a good bit of info. I've got no specific advice for you, but don't expect $125.