How does replay review work once a call is challenged?

All reviews are conducted at the Replay Command Center at MLB Advanced Media headquarters in New York, by replay officials, who are full-time Major League umpires working shifts there as well as on the field.

• Replay officials decide whether to change the call on the field, confirm it, or let it stand because there is no clear and convincing evidence.
• Since 2017 they are expected to decide within two minutes (some exceptions are permitted).
• If a call is changed, the replay official places both clubs where they would have been had the original call been correct.
• If a call is overturned, any decision a manager made after the play that was influenced by the incorrect call is nullified, and the manager may reaffirm or change it.
• The decision is final and not subject to further review. Once review has started, on-field personnel from either club who keep arguing the contested calls or the decision are ejected, and no protest is allowed on a replay official's judgment decisions.

Source: MLB, Replay Review (mlb.com/glossary/rules/replay-review).