Hi there,
I guess this conversation is “slipping off” the original topic 
@Donye the live chat link posted by @Briggsy could be very useful for your needs. This one uses the external service.
Also you can also build the chat entirely in Adalo. You need to study the group chat template, and as @Flawless mentioned, you need to allow users to create with conversation only with you.
When you study the chat template, you can see that when you press “+” to start the conversation, you get to the screen with the list of users. So if you filter out the list of users in a way that there will be only one result - you as an admin, you can stop other users from chatting with each other.
As an “extension” to this logic, you don’t really need to have a separate “Start Conversation” screen - you can rather “convert” the “Start conversation” button into a single-item list of Users, filtered by your email. Please see the answer by @crmorris2 in a thread here: Chat feature in app
Please note - my reply provides not an “end-to-end” solution but rather the path to explore
To better understand how this works, you can search on forum based on “chat with admin” and on YouTube based on “Adalo chat” keywords.
Best,
Victor