CustomPress custom field + add or check http:// is added to all

This is actually for the plugins CustomPress-- Not multisite. my mistake..

Hi, Im wondering if theres an easy way to update the values for all my vendors.

Vendors were entered as custom post type 'Vendor'.

There is a custom field website. Some addresses were entered without the http:// at the beginning.

Is there a way I can quickly make the correction. Also, How can I check at time of entry to make sure correct format is entered?