You can't.
Castling

black k. has moved and white lacks a rook .....u cannot castle. White has one move---tip the king over !

Omg at the above comments. Just bring the rook over the King to f1.
King stays put. It's kingside castling.
Edit, yes, I realised white's king has moved. The white king should've started at g8. Iirc in chess960 both balck and white have to mirror each other across the board.
How would I castle in the following position given that neither the king has not moved.