Heimdall Snapshot Restoration Steps
Overview

The instructions below will fully restore Heimdall's data directory by downloading each file and subdirectories individually. 
Use aria2 or wget to download all of the Heimdall files. Last, modify the ownership of the files so Heimdall can access them. 

wget, which is ultimate command line downloader. However, wget failed to accelerate download speed. 

For ultra fast downloading use aria2.  It is a utility for downloading files. aria2 supported HTTP(S) protocols. 
It tries to utilize maximum download bandwidth. 

Please download the file that will tell aria2c which files to download and which directory to save them to. Then, use aria2c to download all of the Heimdall files.
Backup, Download and Install

1. Stop the heimdall services 

service heimdalld stop
OR
systemctl stop heimdalld.service


2.  Navigate to the directory with your data store in it, then download the file containing which files to download. This file lists each file to download on the first line, followed by which directory to save it to. 

cd /var/lib/heimdall

wget https://snapshots.girnaartech.com/polygon/amoy-testnet/heimdall-amoy-testnet-files.txt

3. Take a backup of existing data

cp -frvp data <destination-backup-Directory>

4. Remove data directory from /var/lib/heimdall

rm -r ./data

5. Open tmux or use screen/nohup to keep downloading after you close your connection.

6. Download the files using aria2c. This will download up to 12 files at a time (-j 12) and will use up to 12 connections to the server (-x 12). The total download size is around 6GB, which can take 30-50 secondes depending on location and latency.

sudo aria2c -j 12 -x 12 --console-log-level=warn --auto-file-renaming=false --summary-interval=3600 -c -i ./heimdall-amoy-testnet-files.txt

OR you can use wget. which can take upto 20 min depending on location and latency. 

Create a timestamp with the current date and Download the files using wget:

TIMESTAMP=$(date +"%Y-%m-%d"); wget -q --show-progress -m -r -nH --cut-dirs=4 --no-parent --reject="index.html*" https://snapshots.girnaartech.com/polygon/amoy-testnet/heimdall/${TIMESTAMP}-heimdall-amoy-testnet/

7. This will download files with current user ownership. Change all files to be owned by heimdall and the nogroup group

sudo chown -R heimdall:nogroup /var/lib/heimdall

8. That's it! Start Heimdall and check the logs.