The application IrfanView is a free tool for converting images. Download from: https://www.irfanview.com/
How to use IrfanView
Menu > File > Batch Conversion / Rename
- Batch conversion setting
- Output format: TIF
- Option > Save Compression : LZW
- Use advanced options > Set new DPI value : 600
- Select input files
- Select output folder
- Click Start Batch
