1. Use the constituent ID to import a constituent attribute
  2. Query on the specific attribute and export out the import ID
  3. You can then use this to import the participants
OR
  1. Add the Constituent IDs to a new import file
  2. Create a query of the records included in this file
  3. Create a Constituent export
  4. On the General tab, click Include, Selected Records, and pull in the query crated in step #2
  5. On the Output tab, select Constituent Information, Import ID and any other fields necessary to identify the constituents
  6. Use the new file of Constituent Import IDs to import the participant records
OR

If the participants are all constituents, Globally Add them as registrants.