I am not sure of your HHI reservation.
If it is one made with HHI points during the 11-month booking window, then you cannot modify it at all by taking out HHI points and putting in AKV points unless that entire HHI reservation time that you already have is separately still available to be reserved by anyone at 7-months out. In essence, if only one of the HHI dates is still being shown as separately available, you cannot do any modification that would take out HHI points and put in AKV points. Your only option is to cancel the HHI reservation and attempt to do the same reservation again using both HHI and AKV points or just AKV points, an exercise likely to fail because, if cancelled, that HHI time that you have could be allocated to someone's waitlist or someone else could grab it during the short time between your cancellation and your trying to do a new reservation. If you were allowed in the past to modify an 11-month reservation with points from another resort at 7-months out, then either the reservation you had was separately available at 7 months out or something happened that should not have happened.
If the HHI reservation was made in the 11-month window, and the day you are seeing open is either the first night or last night of your HHI reservation, then you could reserve that particular night using AKV points, then modify the HHI reservation by dropping the applicable night and then contact MS and have it link the two reservations so you not have to change rooms.
If you made the HHI reservation during the 7-month window, then you can modify that entire reservation to change to just AKV points or a mix of HHI and AKV points. If you do that modification on line and list the applicable contracts to use for it, the system will use any banked points first from all the contracts if there are any banked points, and then use all regular use year points left in the first contract listed, then if needed do the same with the second contract listed, etc. If you want to do any reallocation other than what would result from that sequence, you would need to call MS to do the modification.