Install the plugin by downloading the gplugin file and dragging it in to Geneious Prime or use the plugin manager in Geneious (under Tools - Plugins in the menu).
Once installed, run the plugin by selecting your reads and reference sequence then clicking on Align/Assemble - De Novo Assemble in the toolbar. Flye is available as an option in the Algorithm drop-down menu.
Mikhail Kolmogorov, Jeffrey Yuan, Yu Lin and Pavel Pevzner, "Assembly of Long Error-Prone Reads Using Repeat Graphs", Nature Biotechnology, 2019 doi:10.1038/s41587-019-0072-8
Yu Lin, Jeffrey Yuan, Mikhail Kolmogorov, Max W Shen, Mark Chaisson and Pavel Pevzner, "Assembly of Long Error-Prone Reads Using de Bruijn Graphs", PNAS, 2016 doi:10.1073/pnas.1604560113