In order for this modulation to be easy to understand, I will use the chords in the treble clef only. This modulation will have 4 steps:
1. Establishment of the 1st key
2. A common chord
3. A modulating chord
4. Establishment of the 2nd key with the cadence.
As you can see in the above picture, we can establish C major with a few basic chords (T, S and D). Here I chose the tonic chord, subdominant 2nd inversion chord which resolves to the tonic and the dominant 1st inversion chord which resolves to the tonic.
This tonic chord is a common chord for both C major and D minor - in D minor it's called the chord of the 7th scale degree or the Subdominant of the Subdominant (SS).
Then comes the modulating chord. This usually should be the chord which has a new accidental of the D minor key (either Bb or C# - 7th raised scale degree). It is best to use a dissonant four-note chord for this purpose. I chose II34 chord (that's a 2nd inversion of the seventh-chord of the 2nd scale degree.
The last step is to form a cadence in the new key - that's why you can see tonic 2nd inversion and D7 which resolves to the new tonic.
Try to play this exercise on your instrument. If you know how to do it, you can use four-part texture (SATB) with or without the pedals for the bass line placing the tenor part in the left hand. After this modulation becomes easy, transpose it to G major, F major, D major and Bb major.