A popular "all-in-one" tool for older iOS devices. It has a section for "Apps" where you can import local .ipa files and install them with one click.
How do I install iPA files from my Mac onto the iPhone? (iOS 7.1.2) ipa files for ios 712 top
Sideloadly is a modern tool that works on Windows and macOS to install IPAs onto your device using your Apple ID. Connect your device to your computer via USB. Open Sideloadly and drag your .ipa file into the tool. Enter your Apple ID to sign the app. Click to install. Method 2: AppSync Unified (Requires Jailbreak) A popular "all-in-one" tool for older iOS devices
Many old apps will give "Connection Error" because the security certificates they use have expired. If you are jailbroken, look for a tweak called Checkmate, Store! or Veteran to help fix these connection issues. (iOS 7