Bet flop? Wait till turn? I assume river is a fold?

PokerStars No-Limit Hold'em, $0.50 BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Button ($153)
SB ($83.35)
Hero ($50)
UTG ($49.50)
MP ($50.70)
CO ($57.95)

Preflop: Hero is BB with 6, 7.
2 folds, CO calls $0.50, Button raises to $2, 1 fold, Hero calls $1.50, CO calls $1.50.

Flop: ($6.25) 2, 7, 9 (3 players)
Hero checks, CO checks, Button checks.

Turn: ($6.25) 9 (3 players)
Hero bets $5, CO calls $5, Button folds.

River: ($16.25) K (2 players)
Hero checks, CO bets $6, Hero??