dig up bag, ensure you do NOT open the bag.
I would bless the bag, purify it, you can do this by sprinkling some holy water on it.
collect some dried botanicals, like lavendar, make sure they are dry so they burn.
if you can get an iron mortar, or a regular iron pan. Drop the dried botanicals in and light it.
this is the incantation part, i would advise you make this yourself, as you know your diety etc.
go along with the guidlines of:
i) asking for the aid of your diety then,
ii) Make it clear you want the spell to be annulled and nothing else and what you are about to do, also make it clear that you do not want any added effect.
iii) thank your diety for her/his aid.
after you have done the incantation, throw the bag into the fire (this wouldnt ruin their life or cause any added effect as you made your intent clear).
7) sprinkle the ashes onto the earth, and after, repay the earth by pouring milk over some tree roots, or giving something back to nature.
I hope this helps.