Where can i replace my battery in saudi arabia

Battery service. Apple can replace your iPhone battery for a fee. Their warranty doesn't cover batteries that wear down from normal use.

iPhone Repair & Service - Apple Support (SA)

Click on Get Service > Repairs & Physical Damage > Battery Service > Continue (https://getsupport.apple.com/topics)

See if this helps:

Find Locations - Apple (SA)

Unfortunately, the options appear pretty meager outside of Riyadh.