First, you will need to go to Accounts Payable > Configuration > Business rules > Vendor > Uncheck "Automatically Generate Vendor ID's" - then follow the steps below

1. Get a list of your vendor import ID’s by following these steps
   A. In Accounts Payable, select Query> New> Vendor, Dynamic.
   B. On the Criteria tab> expand Vendor Properties> select Vendor Import ID.
   C. On the Output tab> expand Vendor> select Vendor name.
   D. Click 'Export to Excel' or File> Export.
2. Once you have the Vendor import ID’s, enter the ID’s under the “vendor import ID” header in the sample excel spreadsheet provided
3. In the excel spreadsheet, under “Vendors ID’s”, enter the new vendor ID you would like the vendor to have – Save your Excel worksheet as a CSV
4. Go to Administration > Import records > Select the “vendor” import
5. With the import open, change it from “Import new records “ to “ Update existing records”
6. Mark the “validate data only” Check-box
7. Where it says “import file”, add the import file we saved
8. Next where it says “Use _____ to match records in the import file with existing records” select “Vendor import ID”
9. Go to the fields tab
10.  Under the “field to import” column, you should see two fields, “vendor Import ID” and “Vendor
11. In the drop down tree, double click “Vendor Import ID”, that should bring that under the “import field”
12. Next, select “vendor
13. Select Validate now to make sure nothing
14. Once that’s done, go back to the General tab and uncheck “validate data only” and then select “import now”