If I were you, I wouldn’t use mine.
Using the automatic turn-off of a power bank is „easy“ if it works. But it is not that reliable. The general problem is that you cannot influence at what power level it switches off. It’s built-in, and you have to make that work. For example, I need an LED to prevent my power bank from turning off while the TonUINO plays music. That depends on how full or empty it is. By controlling this LED with the Arduino, I can be more certain that the power bank will actually switch off when I want it to. But if you have a power bank where this isn’t necessary, it could easily happen that something changes and the switch-off function no longer works.
You also need an additional switch or button to be able to wake up the power bank. A button means you cannot turn off the TonUINO without waiting for the timer of the automatic turn off. When you use a switch and use the auto turn off, you need to use it twice because it stays on. So you need to switch it to off first and then back on.
If I were you, I would keep the power bank and use a component that gives you (or the TonUINO) full control over the power supply: Pololu als Power-Switch (Einsteiger). With the Pololu power switch (LV), you can activate the TonUINO with a press on the play button, it can automatically turn off when it’s no longer used and you can also turn it off with a long press on play.