How to charge this lipo back?
That will not work.
Not without extra care, attention and electronics.

If one cell when you start charging is 3.3V and the other is 3.4V, depending on the quality of the cell and thus its internal resistance, already you can have a situation where one cell forces several amps into the other the moment you connect them in parallel. Doing this regularly will severely reduce the life of your batteries. If the difference is larger the currents can be big enough to cause serious and immediate problems.

Apart from that, you should be aware that your device or pack should turn off the current drain once either one of the cells falls below a safe minimum voltage (3.2V for example, or 3.0V), so that they can't discharge to a point where damage occurs. This is why many 2cell packs have an internal BMS board that monitors both cells for over and under voltage and turns them off if either is at danger.

With home-made wearable tech I'd also strongly suggest you add current-limit protection inside the battery pack, so that a single mistake while wearing has a much lower risk of short-circuit based fire and/or injury.