You want to give specific admin access to another mTxServ user in order to let him control your server? Then, follow those steps to add a collaborator:
Access your server's panel
Click on the Advanced section and click on Collaborators
On the right side, click on the gear then Add an admin
Enter the email address of the mTxServ user you want to give access to
Select which permissions your collaborator will have on your server
Eventually, do not forget to check that the username of the added collaborator is correct.
That's it folks!