This sounds close to the genetic algorithm to identify multiple conformers of openbabel (link to the documentation with --nconf to set the number of conformers
obabel startingConformer.mol -O ga_conformers.sdf --conformer --nconf 30
--score rmsd --writeconformers
However I infer your preference of using a GUI is to define which of of the single bonds are free rotors (allowed to rotate). I guess the normal way in Avogadro were to select atom instead (Extensions → calculate → freeze selected atoms) and then launch the algorithm (Extensions → OpenBabel → Conformer Search) and to venture out the options provided there. See here.