A “relation” is a table and a “tuple” is a row.
Here’s a nice shortcut for getting the name of the table from the table id (you can also query the pg_class table):
=> select 17720::regclass;
┌──────────┐
│ regclass │
├──────────┤
│ my_table │
└──────────┘
(1 row)
Now how about the row? The “tuple bit” is a tuple identifier, and every table in your database has a special system column called ctid where those identifiers are stored. Now that we know the table in question, we can do:
=> select * from my_table where ctid='(889,66)';
However! From the system column docs (emphasis added): “[A]lthough the ctid can be used to locate the row version very quickly, a row’s ctid will change if it is updated or moved by VACUUM FULL. Therefore ctid is useless as a long-term row identifier.” In other words, if you’re quick enough you can probably trust that the row returned is the one involved in the deadlock, but that info won’t be available forever.