I would offer them food 5-7 days after the assist, if they do not take it I would assist them again. Repeat this process until they take the food on their own. Once they feed on their own, feed them a slightly smaller meal every 5 days for a month or two just to fatten them back up a bit.
Also make sure your f/t are nice and warm; I thaw mine for a few hours then warm them up in a zip lock bag in hot water until they are warm to the touch.
I have had great success with this approach. Some snakes were taking food on their own after 2 assists, others took 4 months of weekly assists before eating on their own.
Good luck
