I assume u r not using tubeless.
1. Is yours tpu tube? Rotate the wheel to let the valve stem upside down then dip into a small glass of water see got any bubbles around the valve and the valve stem. If have bubbles, apply super glue to seal the leak between the joining area (not on the valve itself until cannot turn the valve later).
2. If using normal butyl or latex tube, u should check your tyre very carefully. The tube take out, pump air, dunk into water to check where is leaking bubbles. Once detected, go back to position of the tyre to check for any super tiny sharp object. Sometimes even need to stretch the tyre a bit to reveal the sharp object that's stuck deep inside and become not quite visible. If too troublesome, buy a new tyre to replace to see if the tyre is the problem. The old tyre no need to throw yet. Coz if it's not tyre problem then at least can keep.