Setting path:
realme UI 3.0 & above versions: Settings > Wi-Fi > three dots in the upper right corner > More settings/Advanced settings > Saved networks. Long press the Wi-Fi name or click the three dots in the upper right corner>Edit, select the Wi-Fi name, and click Remove.
realme UI 2.0 & 1.0: Settings > Wi-Fi > Advanced Settings > Saved Networks. Long press the Wi-Fi name or click the two dots in the upper right corner > Edit, select the Wi-Fi name, and click Remove.
realme UI R & Go & T & S & U Edition: Settings > Network & internet > Wi-Fi > Saved Networks > Forget
Note: After the selected network is removed, the phone will no longer automatically connect to this network, and you may need to re-enter the password when connecting again.