Can depend on the Excel version, but in 2016 on Ribbon > Developer > Insert to put a control on a sheet. You'll get a prompt to assign or create a macro. Create will open the vb editor. The related method would be to create what is called a userForm (not form) in Excel. To keep using the same sheet, you'll have to edit an existing one rather than create, or use one as a template to create new ones.
As an observation the way you declare your variables on one line means that everything that's not explicitly typed (and I don't mean keyboard) is a variant.
e.g. only Src is a string, the rest are variants and you're relying on Access to correctly figure it out when values are assigned.
Dim strPathName As String, mAsc As String, Cust As String, Src As String
not
Dim strPathName, mAsc, Cust, Src As String
unless you intended them to be variants.
EDIT
Forgot to request that for more than a few lines of code, please use code tags (# on forum toolbar) along with proper indentation to make your code easier to read. Also prevents forum from adding spaces at the 50 character mark, which only adds to confusion in code posts.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.