You have to remove the release hook and replace the original sear. It's
an inexpensive part. Depending who did the release, you may have to also
replace the spring in the trigger that loads the sear. Spears, for example,
replaces it with a small rod, so the release hook will be rigidly attached to
the trigger. I have seen release triggers where that wan't done. It is also
likely that the notches in the hammer have been altered.
The gun cannot function without the sear. It will become fully automatic, and
actually become illegal to own. You would be better off buying a pull trigger
and selling the release.