You need to either:
Find a complete copy of the application that's not missing that folder.
Or, if it has a composer.json file, you need to use composer to assemble it. Plesk has a composer tool which can be used for this, or you can follow the application developer's directions (you'll need to do these locally on your PC as most need command line access which we don't offer), then upload the final folder structure that's output by composer.