It should tell you on the label - a 1C charge would be 3800/1000 = 3.8amps, a 2C (if allowed) is 3.8 x 2 = 7.6amps. You'll be safe to use a 1C charge, even if 2C is permitted. Unless these were used, they should have come with some instructions and safety warnings, its worth a few min to sit and read them. There should be some info on how to care for the lipo.
Use charger that's lipo capable, and use the lipo setting, anything else can be dangerous.