how to convert multi distributed GPU to single GPU

[kobrafarshidi]

in this project we should use multi GPU . How to change source code to could use for single GPU systems because when I run this code with system that has single GPU(Geforce gtx ti), I have error and I could not run project.
python -m torch.distributed.launch --nproc_per_node 1 tools/run.py --pretrain --tasks vqa --datasets m4c_textvqa --model m4c_split --seed 13 --config configs/vqa/m4c_textvqa/tap_base_pretrain.yml --save_dir save/m4c_split_pretrain_test training_parameters.distributed True