How to edit initial catalog of connection string in app.config at runtime in fsharp?

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F#

.NET4.5

Configuration

Below is my Sample Connection string:

<add name ="Key1" connectionString="Data Source=localhost;Initial Catalog=;User ID=userXyz;Password=xxxx3" providerName="System.Data.SqlClient" />
Inside which i want to update Initial Catalog=; to Initial Catalog=SomeDBName; all this during Runtime

What I have tried:

<add name="Key1" connectionstring="Data Source=localhost;Initial Catalog=;User ID=userXyz;Password=xxxx3" providername="System.Data.SqlClient">
Inside which i want to update Initial Catalog=; to Initial Catalog=SomeDBName; all this during Runtime