Let's see if someone who understands more than battery voltages can help you.
If you are careful try to charge the battery directly, but be careful, if you pass you can explode.
Ideally, you should do it with a variable voltage source and controlled by an ammeter, so as not to run over the charging current, but if you only have 5V (usb or charger) you can try to charge it a bit by connecting it for two or three seconds, and resting Another four or five seconds, checking the tension from time to time until it passes a little over 3.85V.
Another safest option would be to look for a 3.7V battery charger (it is a voltage common to many li-ion batteries), but if you do not put an ammeter, do it for short periods, although you will not have as many problems as a 5V charger, but maybe it's a bit short, and do not charge the battery a lot.
Eye, if you're not sure do not do anything, as I said the battery may explode. Check that it does not get hot and that it does not inflate and make no mistake with the polarity.
Greetings.