Offline access to Galery?

Product: PowerShell Universal
Version: 5.6.13

I am working on setting up PowerShell Universal on a server that is in an air-gapped network. If I was to download the GitHub repo (GitHub - ironmansoftware/gallery: Public gallery of modules for PowerShell Universal) and transfer it over, what’s the procedure to have its content showing in PSU gallery on the offline server? The readme file says “This repository can be installed with PowerShell Universal v4 by registering it as a module repository.” but I cant figure out how… The registered PsRepository are not showing up in Platform \ Modules \ Repositories