You can use the Edit participants page of a tournament to view and edit players that registered for the tournament.
In addition to the publicly available information like the players' display name and country, this list also includes their ingame names, any custom registration fields, as well as their Discord tag (if they added it to their profile).
You can always edit the display name of any player in the tournament, as well as their ingame name. Players themselves can only edit their registration information while registration is still open, so in case any mistakes come up during the tournament, an admin would need to fix them here.
You can use this page to remove players from the tournament. If you do this before it starts, they will be removed completely, while if you do it during the tournament, they will be dropped.
It is also possible to "undrop" players that were dropped, or dropped themselves. However, this is only possible during the round the drop happened. Once a new round is started, they become final!
If the tournament uses a Custom format, this page allows you to see players’ decklists prior to tournament start, so you can manually check them if needed (since the Custom format does not have an automatic deck check).