How to fix the type or namespace name 'stimulsoft' could not be found in C# WPF

I'm using C# WPF in Visual Studio 2019 with these :

.NetFramework 4.7

Windows Server 2012

Stimulsoft

When I run this line of code when it reaches the report.Render() that will show this error :

  <pre lang="C#">//using Stimulsoft.Report;
        var report = new StiReport();
        report.Load(@"D:\Myreport1.mrt");
        report.Render();
        prtviewer2.Report = report;

Changing Net Framework
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