You can learn from this article how to add permission sets to a user.

1. Navigate to Setup > Users > Permission Sets.
2. Select the appropriate Permission Set for LogMeIn Rescue by GoTo from the available options:
   • Rescue Admin Permission Set: Provides the functionality needed for a Rescue admin. Access to see and modify Rescue Settings object.
   • Rescue Integration Permissions: Provides the functionality needed for any Rescue user. PIN generation and access to Case, Rescue Log and Rescue Session objects.
3. Assign the Permission Set to a User or list of Users.
4. Click Save.