This mod adds 3 commands:
/velocityforward <selector> <speed>/modifyvelocity <selector> <add/set> <x> <y> <z>/startfallfly <selector>
The speed and xyz options are a float
Using the add option for modifyvelocity will add onto the player's current velocity, while set will replace their current velocity with your new values
/startfallfly will trigger elytra flight