If the sole owner has died, do any relatives still have access to the owner’s email account? If so, tell them to follow the instructions in Logging in without setting a password to get an email link to log in to Groups.io under the owner’s email address. After they are logged in to Groups.io under the owner’s email address, they can go to the group in question and change the role of another group member to Owner.
Note: If someone has access to the owner’s computer, it is possible that the owner’s Groups.io account might still be logged in on their web browser if the account’s 30-day login cookie in that browser has not expired.
If no one has access to the owner’s email account or computer, you can contact Groups.io Support, explain the situation, and ask to be made an owner of the group.
Tip: After someone is able to log in to the group as an owner, they should designate at least one other member as an additional owner, to avoid this situation again in the future.