1. Download the QGIS from the link according to your operating system (http://www.qgis.org/en/site/forusers/download.html) and install it.
2. Download the *.GeoJSON file for the area of interest you prepared for field paper/s and store in your drive.
3. Open QGIS > Click on ‘Add vector layer’ (top of left side panel) > browse the ‘*.GeoJSON’ file saved in your drive> Open it.
4. Select the ‘LAYER’ in the table (left side)> Click right button > click ‘Save As’ > Save as vector layer dialogue box opened > choose the ‘.gpx’ format from dropdown list > give desired name in ‘Save As’ box > browse the location you desire to store.
5. You can open the ‘*.gpx’ file in JOSM to see the grid/s and manually draw Girds Number like A1, A2, A3…. And save the file.
6. Copy the ‘*.gpx’ file from where you stored.
7. Connect your android device with computer > open as usb storage device > open ‘OSMAND’ folder > open ‘TRACK’ folder> paste the ‘*.gpx’ file > disconnect your device from computer > restart your android device.
8. Now you can see the grid/s overlayed on the map in your OSMAND. Happy mapping!!!

Thanks

Ahasanul Hoque