To my knowledge, IPAM won't automatically place subnets into groups from a discovery. The groups are used to organise the subnets into a more readable structure, e.g. Sites and breaking it down further into categories like Wireless networks, DMZs, Servers, etc.
If you know your various subnets you could use the Import method with the structure / IP addresses templates and build a structure with groups and parent IDs.
In the example below, the two groups "Test" and "Test 2" are at the top level (ParentID = 0). The Supernet is in the Test group and the 3 subnets link to the supernet as the parent ID. The final subnet has a parentID of 19, which is the ID of the "Test 2" group.
Otherwise you could run your discoveries, import everything in, export the data, delete it from IPAM, massage the data in your spreadsheets and import it all back in again.
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