Heating the veneer, but not hot, hot, will soften the glue, allowing
you to peal it off. You may not need the putty knife as much as you
think. Using a clothes iron will work also, but place a cloth over the
veneer when using an iron.
If you ever have a piece of furniture where the veneer has buckled up,
or bubbled up, heat the area (softening the glue), clamp the veneer
back down and allow the glue to dry again, hence veneer repair. A slow
heating (any heat source) is recommended, and pay attention to your
finish. Too much heat may affect the finish. As long as there is glue
still under the veneer, this repair will work, otherwise, injecting a
tad more glue into the cavity will need to be done.