You want a li-ion boost converter + charging board like this https://www.amazon.com/AITRIP-Lithium-Battery-Charger-Adjustable/dp/B08GWTBD3T

Wire your battery up to the bat+ and bat- pads. Use a multimeter to read the output voltage, and turn the dial until the output voltage is what you desire (probably 5v, unless you plan on powering something external that needs more than 5v, in which case you can use the pin that has a voltage regulator on it).

After your voltage is set, you can hook up the arduino to the +/- out pins. Charging is dome through the micro USB port, or you can solder your own connector next to it if you dont want micro usb