Please follow this process to convert the file in the format the hub will understand:
On Windows, assuming you want to convert a file called ‘in.asc’ or ‘in.tif’:
- Follow the quick start steps to install OSGeo4W at OSGeo4W
- once installed, launch “OSGeo4W Shell” (you can search for it in the windows search bar), this will open a command line window
- ensure that the input data file is in the command line’s working directory
- optional step if you have a tif file, convert it to asc with this command: gdal_translate -of AAIGrid in.tif in.asc
- type the following command: gdalwarp -s_srs EPSG:27700 -t_srs EPSG:4326 -of vrt in.asc out.vrt
- then type the following command: gdal_translate -of AAIGrid out.vrt out.asc
- out.asc will be in the correct format for the hub
If you are on Mac, please check this link for installing gdal installation - Installing GDAL on MacOSX? - Geographic Information Systems Stack Exchange