On a baroque descant/soprano recorder (the one most players start with) the standard fingering for the low F# is thumb + the 1st, 2nd, 3rd, 5th, and 6th holes. (0 1 2 3 - 5 6 -) If you have a German recorder you need to add the right hand pinky so the fingering is then 0 1 2 3 - 5 6 7.
The high F#, one octave higher, is produced by overblowing and using this fingering: half thumb, 1st, 2nd, 3rd, and 5th holes (Ø 1 2 3 - 5 - - ) The corresponding fingering on a German recorder is Ø 1 2 3 - 5 - 7.
There are fingering charts for the recorder at several places online. Here is one for the baroque recorders in C: