What do you mean by “bulk import method?” Are you referring to importing bank statements or the Batch Create function?
If you are referring to importing bank statements, you can use bank rules. See the Guide: https://www.manager.io/guides/9243.
If you are referring to Batch Create, suppliers are represented by hexadecimal UUID’s rather than plain language. So you must first make manual entries covering all desired suppliers. Then, partially complete a Batch Update to see the UUID associated with each specific supplier. Following that, you can insert the appropriate UUIDs to designate suppliers while doing a Batch Create.