How can I use my iPad find my device to find my phone

Check to see if there is a Find My app already on the iPad.

If not.......

Open Safari

Type in www.icloud.com/find

Enter the Apple ID and Password of the phone

If the phone shows as "Offline", the battery has run down or the phone does not have an Internet connection where it is currently located.

All that you can do is keep checking a few times each day to see if the status of the phone has changed.

Some more info on FindMy is available here:

Find My - Official Apple Support