DirectAdmin allows one IP# per account.
1. Do you have an available IP address at the reseller level? If so, just assign it to your second user.
If not, do you have an available IP address at the admin level? If so, then assign it to your second reseller and go back to number 1, above.
If it's not your server, then you may need to contact your hosting company. If you don't have any IP#s and it IS your server, then you may need to contact your upstream connectivity provider.
Jeff