As far as I know "Al tun tun" is used to say that something is being done in a hurry and without much effort.
See the tuntún, do something to the tuntún.
In Argentina, tun tun means without order, without an organization
In Colombia it means raised on the back, take it to the back or tuta. It is also a colloquial way of meaning carelessly, without care or without the necessary analysis, without thinking. It is also said to the guachapanda.
Doing something to the tun means doing it without thinking too much about the consequences and randomly, without a preset order. Expressions that mean something similar could be to do something crazy or ton-free and are not.