Use touch /home/pi/wifi-reconnect.sh to create shell script file, with following content:

#!/bin/bash 
 
SSID=$(/sbin/iwgetid --raw) 

if [ -z "$SSID" ] 
then 
    echo "`date -Is` WiFi interface is down, trying to reconnect" >> /home/pi/wifi-log.txt
    systemctl restart wireless 
fi 

echo "WiFi check finished"

chmod +x /home/pi/wifi-reconnect.sh

sudo apt-get install cron

Use sudo vim /etc/crontab to edit crontab

By putting following content at end of file:

* * * * * root /home/pi/wifi-reconnect.sh

Test it by disconnecting from WiFi:

sudo ifconfig wlan0 down

Script should reestablish connection within 1 minute.

After the RPi reestablish connection, reconnect RPi and check log file: /rcat /home/pi/wifi-log.txt