Assuming, this question is regarding SSIS, you can follow below steps -
1. Right click file connection Manager and select Properties. Alternatively, you can select file connection manager and press F4.
2. Select browse button (three dots) against “Expressions” property.
3. Select “ConnectionString” under Property and click on browse button, it will open expression builder.
4. In the Expression box, drag the variable which contains complete file path.