Welcome to Cheftalk Tashana,
I am thinking too much moisture, the juice from the strawberries. When you cut them did you absorb some of the moisture with a paper towel ?
Usually when they sink there is not much you can do about it. I would put them back in the oven for 5-8 minutes , let them cook through and use the cupcakes for a layered dessert.
Break up the cupcakes and use the cupcake layered with cream in a bowl. Looking like a trifle but without the custard. At this point you can add the strawberries with the moisture in the layers. This is one suggestion, maybe there are others. ...just a thought, Petals.