Revalidation of expired itunes Gift Cards

I hope that I've found the right site to convey this appeal............

Can someone please let me know how I may revalidate 3 No. expired £15 itunes Gift Cards which were mislaid but have now been found in a drawer.

One of the many problems of the ageing process is forgetfulness and I would prefer not to lose £45 worth of value now that I've recovered the Cards,

which were Birthday and Christmas Presents, and therefore, no receipts.

I hope all is not lost and that I can be given instructions to get the matter sorted out soon.

Thank you for your help.