Reset password of admin account on qnap mattermost

Hi, we have the Mattermost application installed on our Qnap. Unfortunately, those who installed it at the time, is no longer there and is no longer available, and we do not know the main user to be able to manage users, create them, delete them etc … How can we recover the information of the administration account by Mattermost? We have full access to the nas as admin.

Through the guide of Mattermost, we cannot understand the command or procedure to be carried out to do a sort of reset of the main account, of course without deleting the history of the chats in place.
Thanks to everyone who can answer. Of course I opened a ticket on qnap, but it tells me to ask here …

You could use this command to promote someone to an admin Command Line Tools — Mattermost documentation.

I believe the listed commands are not suitable for qnap. i should enter mattermost console … from qnap. How could I do?

I understand the mistake. Mattermost is installed on qnap, in docker format, therefore to access it, you must first start the docker instance with:
system-docker exec -it mattermost_app_1 /bin/sh

Then, you can use the mattermost commands found with the command:
bin/platform -help

Hope this helps someone else