As a start always make sure you're updated to the latest SDK available on the VRChat Website.
We DO NOT recommend using a provided SDK within an avatar package, these could be out of date or lead to broken scripts.
If you have Index controllers you do not need to worry about hand animations, any other controllers or desktop use will have to be fixed with this method.
PLEASE NOTE THE FOLLOWING:
- Some avatars will not have the specific name of the FX or Gesture layers.
- The animations for hands could be on either layer, make sure you find the correct animations.
- If an animation has "Body : Skinned Mesh" do not copy that over to the other layer, that is a blendshape for you're facial animations.
- You may have to copy the hand animations from the FX layer and paste them on the Gesture layer instead of what is shown here.
The avatar use in demonstration is Dakota, while this avatar shouldn't have issues with the hands, it is still the same process to fix.
First make a duplicate of the Avatar you're trying to fix. (Right click the avatar in the Hierarchy and click duplicate)
On the Duplicated avatar, it should have a (1) behind the name, located in the Inspector Tab there is an Animator section where it says "Controller" you will add/change this to the Gesture or FX layer on your avatar to make it the active animations.
Once you have done that, go to the Animation Tab (to open; at the top click Window>Animation>Animation)
Within the drop menu located with the name "OPENHANd left" here, Select the hand animation you're going to copy from.
The default hand animation names will be; Open, Fist, Peace, Rock n Roll, Point, Finger Gun please take into consideration you may not have the same names shown in the pictures.
After selecting all of the hand animations from this gesture, hit Ctrl + C to copy. Sometimes you may find a Yellow coloured text, this will not impact the animation and you do not need to copy it over.
Back within the Inspector Tab, change the Animator Controller to the FX or Gesture layer on your Duplicate avatar.
Go to the Animation Tab once more and within the drop down menu named "Open" here, select the hand animation you copied and hit Ctrl + V to paste in the animation. If done correctly for example, your Openhand Facial animation and your Openhand-Hand animation should work as intended in game.