Newbie help needed please ! 

I'm trying to set my property 'Phone' according to the value of 'Vendor' and can't get anywhere with the syntax.

I imagine for every value of 'Vendor' I will have to make an 'if' and 'then' argument.

A little help please ? ...... yes I'm asking you do do my work ! 

Thank you in advance...... as you can see, I didn't get far:

Sub main()

Set swApp = Application.SldWorks
Set ModelDoc = swApp.ActiveDoc
Set CusPropMgr = ModelDoc.Extension.CustomPropertyManager("")
'Add custom property if not already there
retval = CusPropMgr.Add2("Phone")
'Change value
getinfo = CusPropMgr.Set("Vendor")
    if = "MCMASTER CARR", then

End Sub