.NET Framework 3.5 Features – Installation of one or more roles, role services, or features failed.
The source files could not be found. Try installing the roles, role services, or features again in a new Add Roles and Features Wizard session, and on the Confirmation page of the wizard, click “Specify an alternate source path” to specify a valid location of the source files that are required for the installation. The location must me accessible by the computer account of the destination server.
Click on “Specify an alternate source path“
Browse for Sources folder path.
Continue the installation.
Or you can run below command to do the installation also.
dism /online /enable-feature /featurename:NetFX3 /all /Source:d:\sources\sxs /LimitAccess
/Source will be the Windows installation disc or windows installation file path.