You must pair your devices to your iPhone before you can use them with it. And, if they have previously been paired with another phone or other device you may have to factory reset them, as most devices have a rather small limit of how many simultaneous pairings they can hold. You will need the manufacturer’s manual or website to learn how to do that, as well as put them in pairing mode. Here are the instructions from Apple’s side of the process→Pair a third-party Bluetooth accessory with your iPhone, iPad, or iPod touch - Apple Support
And perhaps you can solicit assistance from a grandchild😁