This means that, from Monday, if you have any fiat currencies remaining on a wirex prepaid debit card they will be automatically converted into Bitcoin at the current exchange rate and transferred into your wallet. No action from you is required.
They've stated that further details will be published in a blog post next week, so I'll keep you up to date on what's going to happen next. Let me know what you think about Wirex and this latest update in the comments down below.