The Spring action in a tweezers is a result of the back end of the
two parts of the tweezers being rolled down on a Rolling mill before
they are riveted or welded together. You have softened this and it
can be revived by rolling this again but you may damage this
completely unless you are able to take them apart.
A pair of Cross lock tweezers costs between 2.00 to 3.00 dollars it
may not be worth your time.