Visit my.sonatype.com for documentation on Nexus Repository version 2.
Importing into Repository Manager 3.23.0 Pro and newer
To import a Maven 2 format repository from a Nexus Repository 2 repository storage directory or equivalent Maven repository layout on disk ( ie. local ~/.m2/repository ) into 3, create a Repository - Import external files task and run it.
More information can be found in the help docs for repository import.
Exporting from Repository Manager 3.24.0 Pro and newer
To export components out of a Repository Manager 3 instance.
More information can be found in the help docs for repository export.
Third-party Unsupported Export / Import Alternatives
Import into Nexus Repository 3.22.1 and earlier, including Nexus Repository 3 OSS and Nexus Repository 2
There is no formal repository export or import built into these versions. You might be able to use third-party tools to do this over HTTP using standard request paths.
Option 1. Here is an example of a third-party tool that claims to do this.
Option 2. Another option is the transfer artifact command of the RiotGames nexus_cli.
Problems with the above third-party tools are to be directed to the tool author.