Have you tried creating a module package for this module? (when you click the edit pen for the extension, you should find a "Create package" button on the top right).
Take care to include the assembly/assemblies needed, and also the Sql Server scripts to install the module correctly (often found in the module folder under Providers/DataProvider/SqlDataProvider/*.SqlDataProvider). There might be other files in the module folder (images, css, etc), be sure to include them in the package, then try to create it. You will find the ZIP file under /install/Modules then, move it away from there somewhere on your local file system (otherwise the installer might try to install it with the next update). Then try to update the extension in a testing system, check if it works and you're done. If there are errors it might be that you are missing some files that have to be included. Check the error messages, and restart.
There used to be a way using the /Install/Module/ folder (put ZIP file there, then call /install/install.aspx?mode=installresources) If you are on an old version of DNN (7 and earlier?) you can still use this. But you've got a load of security issues that should drive you to upgrade.
I don't know of a good way to do this now. For security purposes DNN removes the Install resources after an upgrade.
IF you already have the module installed in both locations, you could copy the resources for the file from server to server (DLL in the BIN folder and the contents of the desktopmodules folder) assuming you don't have any MANIFEST file changes that need registered.
