To acquire the access to ScanNet dataset, Please refer to the ScanNet project page and follow the instructions there. You will get a download-scannet.py script after your request for the ScanNet dataset is approved. Note that only a subset of ScanNet is needed. Once you get download-scannet.py, please use the commands below to download the portion of ScanNet that is necessary for ScanRefer:
python2 download-scannet.py -o data/scannet --type _vh_clean_2.ply
python2 download-scannet.py -o data/scannet --type .aggregation.json
python2 download-scannet.py -o data/scannet --type _vh_clean_2.0.010000.segs.json
python2 download-scannet.py -o data/scannet --type .txt