Swapping cow skin head to different congas

I am hoping that somebody might be able to help me out.
I have just purchased a new set of congas. They came with Cow Skin heads that had been used on the congas for the last seven years. Still in very good condition. I wanted to swap those same cow skins to another set of congas. Although the dimensions are the same the cow skins had become too wide at the top to fit on the second set of congas. Over time they had obviously stretched to such an extreme, the flexibility and 'bounce back' had been lost.
Can anyone give me some suggestions (hopefully that you have put into action) that can help me re-skin these cow skin heads onto my second set of congas.
Regards
Toby
I have just purchased a new set of congas. They came with Cow Skin heads that had been used on the congas for the last seven years. Still in very good condition. I wanted to swap those same cow skins to another set of congas. Although the dimensions are the same the cow skins had become too wide at the top to fit on the second set of congas. Over time they had obviously stretched to such an extreme, the flexibility and 'bounce back' had been lost.
Can anyone give me some suggestions (hopefully that you have put into action) that can help me re-skin these cow skin heads onto my second set of congas.
Regards
Toby