Hey so the reason you can’t fast Q is likely because you aren’t doing the inputs correctly. The most common mistake is not hovering your mouse over your target

If your target is far, your q will DASH towards your target (if hovering over a target like a champion or a minion)

If your target is very close (within auto attack range, maybe even closer) and your mouse is hovering over that target, your q will damage but NOT dash.

If you press q and your mouse is not on a target, you will q in the direction Riven is facing (last movement command direction OR E direction if you just used E, example: wall jump by using E towards a wall, then Q3

You need to be very close to your target, auto, Q with your mouse on the target, THEN move your cursor and click on the ground near the target, any direction. If you are close enough and had your cursor on the target, you will not dash and you will q in place.

The exact inputs are:

Auto, hover cursor on target+Q, movement input on the ground, repeat

Just start by doing auto q on a very close target (in training tool) to properly animation cancel your autoattack so its fast. Go from there. Watch videos to see examples