Cannot find package NETCore

I’m just starting a project and getting this error: Severity Code Description Project File Line Suppression State
Error NU1102 Unable to find package with version (= 3.1.18)
- Found 56 version(s) in [ Nearest version: 5.0.0-preview.1.20120.5 ]
- Found 0 version(s) in Microsoft Visual Studio Offline Packages Project1 C:\Users\jgedr\source\repos\Project1\Project1\Project1.csproj 1

I don’t know how to correct this problem; also, version 3.1.18 isn’t listed. Please help.

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