How to restart hostapd

I'm currently experiencing this issue on a openwrt 18.06 router that I cannot upgrade in the next few weeks.
It is suggested to restart hostapd, but I don't know what this means. Eventually I found that it is a script:
but when i run it from the command line I get:
/bin/ash: ./lib/netifd/ Permission denied
So, my question is: how can I restart hostapd?

With the wifi command.
But it would be better to investigate the reason for the instability, rather than papering over it.