Upgrade from contracts-ethereum-package to contracts-upgradeable on existing contract and got error "Proxy admin is not the one registered in the network manifest"

[leckylao]

As mentioned on Is it safe to upgrade from contracts-ethereum-package to contracts-upgradeable on existing contract. The new deployProxy wouldn't work with old contract that written in contracts-ethereum-package. Which would raise The requested contract was not found. So have to use the existing deployed one.

@abcoathup

When you test an upgrade on the fork (without first doing a deploy), the ProxyAdmin for your proxy isn’t registered in your network file.

Where's the network file? Is there a way to register it manually?