Create New Script using interface, configure, save and run.
CHECK script.m file.
ping1 is a destination for your first ping test ping2 is a destination for your second ping test pingCount is a quantity of pings in one test lossLimit is a limit for "down" notification interval is a interval within each ping
With my predefined config you receive a notification if your ping1 and ping2 tested by 50 times with a 150ms interval and loss is more than 80%.
You can change variables by yourself.
Please set new /ip route for destinations you want. USE MIKROTIK DOCS FOR INFO.