sounds like a classic case of stiffness in the wrist (carpal hypomobility). if it isn't painful you may be able to just force it in all directions and stretch it out. this would imply pushing it in all of the six major directions until you felt about a moderate stretch. the length and intensity of each stretch is up for debate and probably dependent on a lot of variables. this also may not work sufficiently as it may not accurately stretch out all of the individual joints in the wrist. i am also assuming you feel the tightness in the wrist and not the forearm when i say that.

however, and this is a big however, the stiffness is more likely to be helped by mobilizing joints in the wrist (and possibly at least one in the elbow). yet, there are lots of joints in there and evaluating and treating it properly should be done by a trained (and good) physio. i don't know about were you live but where i live lots of physios are bad at treating the wrist. i'd see if you can find a certified manipulative physio or a certified hand therapist of some sort. i could be off on that idea.

there are some relatively easy things you could do to see if it increases your movement and decreases your perceived stiffness. for example, "slide" the hand, the whole hand, in the exact opposite direction you move it into. let me explain that more. as you move the palm toward the anterior aspect of the forearm or inward in that hand shake position i previously described, you can stretch the hand by pulling it out from the forearm (as if to stretch the arm and make it longer) or glide/slide it straight inward (not an angular movement like what you used to get the hand into that position but rather more of a translation as if to slide it off the forearm and not just pivot while still attached). that may be tough to follow and certainly isn't the most well organized though, sorry about that. pictures would be best. anyway, in reference to that hand shake position, if the hand moves down to the floor you'd want to slide the hand up to the ceiling and always in the opposite direction for each movement. that should help stretch the wrist.

that having been said the wrist is a very intricate and complicated area that requires an intimate knowledge of underlying anatomy when treated. it may not be the type of thing you want to treat yourself. did you see a physio?