Move from android after intially declining
You have to wipe the phone to get the assistant to run. It won’t merge content, just import on to a blank device.  Make a backup if you want and then in settings, erase all content and settings. Then you can run the Android import and get all the migration done and review. 

Worst case, you examine the data, sync or export contacts and apps and then erase / restore your current backup and merge the data.