Hi Bill,
Welcome to our community ! 
there is a default API call to aggregate a single account, please look at: https://community.sailpoint.com/t5/Technical-White-Papers/IdentityIQ-REST-API-Integration/ta-p/76814#toc-hId-1564478197
If you want to start an aggregation task, you can take a look at:
https://community.sailpoint.com/t5/IdentityIQ-Forum/SCIM-REST-APIs-to-launch-cancel-tasks-i-e-not-workflows/m-p/28862
If you have any further question, please let us know
– Remold