[ubuntu] Repeare a virtual usb stick on a VM

Hello everyone,
i am working on a VM ubuntu and i am usint a virtual USB stick. Since my last update i can't access anymore my usb stick . When i am looking in the permissions i see this:
owner: root
group: root
others:
How can i change the groupe to vboxsf? what are the commands in terminal to put??
As you notice i am new on ubuntu:) need help pls!!!
TNX