You may use soap solution to check leakage.
If the air is leaking from inside valve, you will have to get the valve pin tightened with a special tool available at puncture shops.
If even after tightening leakage continues, you can change only the valve pin. It’s about 20₹, available at any automobile spares shops. Chances of it happening are low, however, if there is some issue, the air leakage will be quicker.
If there is a puncture in the tyre, check and get resolved through Ather service/Puncture shop.
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