Do gentle flexing exercises, a soft, small ball is great for this.
Get a stress ball and squeeze it for about ten times then relax for 4mins then repeat but take it easy as it can take a long time before a injury like that to heal
To reduce swelling , which can make any exercise more difficult, raise your hand above your heart level using a pillow when in bed and during the day use a sling to hold it up.
For the stiffness, if you have access to a vibrating exercise machine do
about 10 minutes daily at low vibration, holding the handle using the "other"hand only.
Any bending, flexing exercises for your fingers and hand must be done very gently at first and gradually increase intensity.
The rule of thumb is to avoid any painful exertion. Easy does it!
It will take some time, so please be patient.
I broke my wrist 5 years ago (wiped out cycling) but luckily had no nerve damage and healed real fast-no cast,no pain killers other than 30% DMSO rubs and self-hypnosis.
Best wishes,
Niko