Patch Base can import sysex files that contain saved patches that you may have downloaded online, or saved from another program, as long as they are sysex files in the synth's native format (i.e. not a file format specific to some other 3rd party editor).
To import a sysex file to Patch Base, simply place the file in the correct folder in Patch Base. This can be done via either iCloud Drive (if you use iCloud to back up your Patch Base files), or via the Files app in iOS 11 and later.
In either Files or iCloud Drive, find the Patch Base folder, which is the main folder for the app. Inside this folder you'll have a "Modules" folder, and inside of that folder, you should see a folder for every synth you've added to Patch Base. Within the synth's folder, there will be a folder for each type of sysex file that the synth uses.
For example, here's the folder structure for the Roland JV-1080:
So, if you had a single JV-1080 patch file, you could just put it in the "Patches" folder, and it will appear in the patch browser in Patch Base. Or, if you had a JV-1080 patch bank file, you could put it in "Voice Banks" to access the bank file in the app.
Please note, the folder for a sysex file type won't be created until at least one file of that type has been saved in the app. So if you don't see the folder you want, just save an init file from the app, and it should appear.
The "Temp" folder holds temporary patch/bank files that store the editor's most recent state. The folder is not directly accessible when using the app, and should be left alone.
If you're a user of Opcode's old Galaxy patch librarian, and you'd like to convert those libraries/patches to sysex files (which can then be used in Patch Base or any other more modern editor/librarian), get in touch with Deep Signal Studios. They provide conversion services for your old sounds!