in SQLite table-name.column-name is a valid expression, but raises "no such column" error

I'm trying to update the "score" column in table Candidate from table "scores" with columns candID centreID score but query

INSERT INTO Candidate (score) VALUES (scores.score)

gives error in statement:

no such column: scores.score

The SQLite schema expr suggests scores.score is valid. SQL beginner very grateful for help.,