Assuming the withdrawal is still in your list of downloaded "For Review" bank transactions, I would TRANSFER the withdrawal to a new cash-in-hand account, called something like Event Float.
You will probably do these events again, so keep the account active. If you decide to stop doing events, then transfer the money back to zero the account.
Just noticed that you are using QB Self Employed. I don't use that version, so not sure whether the options are the same and you can access your COA, so this might be totally useless!