Should a gift presented to an administrative employee be returned after it is known to be a bribe upon consulting the manager, especially since the manager initially approved it and then recanted?

The gift given to an employee for their mandatory work is ill-gotten gain (ghulul) and it is impermissible for them to take it, unless their employer authorizes it. If the manager permits you to take it, then there is no harm in it for you. However, it is more preferable and safer to give it away as charity, so that your benefiting from it does not lead to showing favoritism to the one who gave it to you, as Umar ibn al-Khattab did in similar incidents where he would pass on gifts to others.