Looking for an app that can open+use automatically another app

you most likely will not find an app that will dial a specific number automatically.

you can use something like tasker:https://androidforums.com/apps/tasker.704/ to create a schedule for a specific app like the phone app to open. unfortunately you can'y use it to make the app make a specific phone call.

 

There's a few auto-schedule-dial apps, but as far as I know none open another app to dial a number.

Here's an example of such app.
https://play.google.com/store/apps/details?id=ru.lithiums.autodialer&hl=en&gl=US

 

Check out macro droid.

https://play.google.com/store/apps/details?id=com.arlosoft.macrodroid

According to the macro settings it will make a call.

 

I use MacroDroid and yes, you can set it up to dial a number at a given time