The article outlines the steps How to set a calendar for a vendor. (Please note to perform this action you require the "manage customers and vendors" permission)
FOLLOW STEPS BELOW:
1. Via the Navigation pane click Administration->Vendors
2. Double click on the vendor you would like to set a calendar for.
3. Select the calendar you would like to assign to the vendor from the calendar drop down list.
NB. For a quick tutorial watch below
