Handle styles (To handle soundfonts change the word "styles" to "soundfonts" in this text.)
In the current version of iOS13/iPadOS13 One Man Band will not appear on the list of apps where you can copy a file to, use a PC or Mac to copy files as decribed at the bottom of this page.
When you touch the Styles button in the top of the main view, you will be presented with a list of styles that you can select from. If you select one it is loaded and you return to the main view. If you instead touch the folders button you will see a list of folders with styles. Intially there is only the One Man Band folder with 60 styles and the empty Downloads folder.
When you copy a single style to One Man Band (download, Mail, iCloud) it will be placed in the Downloads folder. When you copy a zip-file with styles to One Man Band then the included styles will be placed in a new folder with the same name as the zip-file. There are many zip-files with styles available on the internet.
Press the Edit button to move the styles. In the Folders view you can rename or delete a folder or create an new one. Select one or more folders before you touch Delete or Rename. Inside a folder you can select multiple styles and then touch Share, Cut, Copy, Delete or Rename. After Cut or Copy you are presented with the list of folders, select where you want to place it and then touch the Paste button. After Share you can select from one of the share options.
Copy files from a PC or Mac computer.
You can use iTunes (or Finder in MacOs Catalina) to copy files from PC or Mac. First unzip the file with styles into a folder with the same name. When your iOS device is connected to the computer you will see a tiny symbol of it at the top of the iTunes screen. Click on it. Then click on the One Man Band app. You will see folders with the name Styles and Soundfonts. You can't look inside those folders. Now copy the folder with styles from the file browser on your PC/Mac to the Styles folder in the One Man Band Folder. If that works the folder with styles will now appear if you check the One Man Band app on your iOS device. Depending on the OS you are using the folder might be placed in the root folder of One Man Band instead of the Styles folder, you can't access it there on your iOS device. In that case drag the complete Styles folder to the file browser on your PC/MAC, add the extra style folder there and then drag the complete Styles folder back to the One Man Band folder. Confirm to replace it. This method (if available on your OS) can also be used to reorganize styles into different folders.