It is required to use a separator between values in multi-select fields. As default, separator is set to pipe "|".
The delimiter can be customized into another single character in Import Assistant > Import Options > Advanced Options > Custom Multi-Select Value Delimiter.
1. Navigate to Setup > Import/Export > Import CSV Records.
2. On Scan & Upload CSV File page:
- Import Type = Relationships.
- Record Type = Leads Only.
- Choose CSV from own PC station. Once user is satisfied, click Next.
4. Expand Advanced Options menu and set desired value in Custom Multi-Select Value Delimiter field and go to next step by clicking Next.
5. Map all fields from the CSV file to NetSuite fields and continue by clicking Next.
6. Initiate the CSV Import by entering Import Map Name and clicking Save&Run.
Solution steps above describes CSV Import of new Leads records. User can take identical step when importing different records. The user is just supposed to select appropriate values on Scan & Upload CSV File page.
Please, be aware that update of multi-select field will automatically overwrite previous values in respective multi-select field. Therefore all intended data for import have to be contained in CSV file (including previous selection).
There is an Enhancement 166404 to have an option to retain previously selected values when updating a multi-select fields.
See also SuiteAnswers article CSV Import: Correct Format when importing records with Multi-Select Value Field.