Condolences on the loss of your partner.
If there's not a lot of credit there then just use up the minutes left on the unwanted plan and cancel the plan. It's not, to my knowledge, feasible to transfer credits although it may be possible in the case of a recent bereavement to get a refund on unused minutes.
Have you been in touch with the TalkTalk bereavement team as they're capable of managing everything consequential on the loss of an account holder.
