You should be able to tell when the gains occurred. Most likely the gains were for 2023 but look at the statement. It shouldn't be hard to figure out since you should have access to your account information which most likely has monthly reports.

You don't need to report Roth gains for income taxes so the question most likely is moot, but double check your records. I don't think you need a 1099 on a Roth unless you are withdrawing from it. Roth accounts are typically not subject to any taxes. That is the whole point of the Roth account. No tax on gains, no tax on withdrawals.