Use the API method:
https://hostetski.ru/panel/apidoch.php#5

Once you need to ask support for unique key to access the API, don't give it to anyone!

EXAMPLE

To reinstall via a browser, follow this link:

https://hostetski.ru/api/reinstall.php?userid=1111&apikey=22222222222&orderid=3333&os=ubuntu-20.04-standard_20.04-1_amd64

Where 1111 - your billing ID (you can find it on the top right by clicking on the spaceman icon)
Where 22222222222 - your unique API key (you can view and change it in the settings)
Where 3333 - the number of your order on which the OS needs to be reinstalled.
Where ubuntu-20.04-standard_20.04-1_amd64 - the name of the distribution.

Replace the data in the link with your own.

List of available operating systems:

alpine-3.13-default_20210419_amd64
centos-6-default_20191016_amd64
centos-7-default_20190926_amd64
centos-8-default_20201210_amd64
debian-10-standard_10.7-1_amd64
debian-8.0-standard_8.11-1_amd64
debian-9.0-standard_9.7-1_amd64
fedora-33-default_20201115_amd64
ubuntu-16.04-standard_16.04.5-1_amd64
ubuntu-18.04-standard_18.04.1-1_amd64
ubuntu-20.04-standard_20.04-1_amd64
ubuntu-21.04-standard_21.04-1_amd64


WARNING

After reinstallation you will have a completely clean OS and need to install the correct DNS and allow SSH login.

- Allow login via SSH:
Login to the Proxmox control panel (login details can be found in the ordering information)
Open the file `/etc/ssh/sshd_config`.
You can use the editor nano or vim.

nano /etc/ssh/sshd_config
vi /etc/ssh/sshd_config

Find the following line (or similar) there.

#PermitRootLogin prohibit-password


It should be reduced to the following form:

PermitRootLogin yes

Next, restart the SSH server with the following command:

service sshd restart # For CentOS/Fedora
service ssh restart # For Ubuntu/Debian

or restart the server.

How to solve the DNS problem is described here:
https://hostetski.ru/panel/billing.php?do=faq&group=9&fgroup=0&item=53